Split tasks, look out for each other. What can I say? The in-game characters can't always help prevent deaths in a direct way by conjuring objects, but real-life people can alert you to incoming elevators, safe passages, and dangerous problems.
I highly recommend playing co-op just for these reasons.
It will make your life easier. It's a game after all, so might as well have fun and relax.
This game supports Local Co-Op ONLY. Meaning your friend needs to grab a separate controller and be right nearby a screen, which is probably yours, but don't quote me on that since I have not tried it (I didn't realize they supported it until I started writing this guide, actually, and that's kind of sad).

This will be an ever-changing section that covers what will make your life easier in-game.
Most of this involves the character combinations you bring with you, but also what items you bring between stages.
I will try and compile specific shortcuts based on these characters, but the 1st section will involve other factors.

Things you can do to make your life easier
-Don't let your characters go empty-handed. Everyone has the ability to hold an item. An exception being the knight and Excalibur (the item drops out of his hand and becomes un-interactable after that stage). Most items that you might consider are crowbars, buckets, wrenches, and hotdogs. These items appear in more than one stage and typically require some extra work to obtain in that stage. It's been noted that you can skip the side-quest in the Zoo by bringing a hotdog from the GIftshop stage. This is one of many examples you may find through your journey.

Characters that will help make your life easier
-The Scientist can hack through computerized doors and gates, eliminating the requirement of having EVERYONE come to stand on the pressure plate.
-The Monk can teleport items to him, eliminating the requirement of walking TO that item and pressing E to pick it up. Strangely, he can "pick up" the parrot on the Island stage using Q while the parrot is nearby. Thus you don't have to go fetch the crackers.
Use Shift to walk and complete his stage efficiently.
-The Twins can be 2 places at once, provided they're within a certain distance (usually on-screen). If you see 2 nearby switches or pressure plates, the twins can handle both of them - so you have 2 alternates with the freedom to proceed.
-The Adventurer has such good rock-climbing abilities, that stages other than the desert will sometimes have a place for her to grapple. You can avoid the spike pits just below the Giftshop by bringing her along.
-The Time Traveler can phase through obstacles provided they are both on the same patch of flat ground. She can proceed past minor rocks and doors and bring back mission-critical items.
-The Hillbilly can breath underwater, letting you relax more because he's not drowning - he's just able to take more time to do things underwater. He's handy in the zoo, and Giftshop levels, since they both involve running errands which require diving.

Know your Causes of Death – Generic Stages
For each character and level, there's a set of factors that can affect whether you come out alive, or have to ragequit (well, you don't HAVE to be raging but...).
THIS SECTION CONTAINS SPOILERS. YOU HAVE BEEN WARNED.


Be careful when jumping down the cliff, past any waterfalls....AIM TO BE IN THE MIDDLE. DON'T JUMP OVER NEAR A WALL OR YOU MAY LAND ON THE GROUND AND DIE!

ANY DAMAGE YOU TAKE IN THIS GAME IS AN OHKO. In other words, you instantly die. In some ways, that makes this game harder than others. In other ways, it's just as hard
You can complete the generic stages with ANY character combination. However, you may have an easier time with some rather than others.
Keep in mind the Instant kill button (9) will void your no death run... and you will have to restart. Also, dying...you cannot go back to a previous save file. Just restart the game.
The main problem with no-death runs is that you're not just grinding through obstacle courses, but the storyline as well. This requires you to be alert, since you're switching back and forth with stuff.

1) Gift Shop/ Crystal Cave Monster
COD: Spike Pits, Hungry Monster

Other possibilities: Electrocution, Falling Damage, Going past the large spike pit without capturing the Crystal Cave Monster, Suffocation & Blast damage when recovering trinkets

Prevention:
Make sure you get the bucket from the well and put it on the fuse box (requires crowbar from starting platform), make nice, clean jumps from either side of the spike pits. Approach slowly, press the space bar AND the left or right key at the SAME TIME. When you're near the spike pit with the big stick in the middle, go JUST past the bell, toward the spike pit and press E (WHILE HOLDING THE HOTDOG). Now, leave the character right under the bell. Next, position a character WITH THE FUSE up above, insert the fuse box and go towards the control panel. Switch to the character at the bell. Ring the bell. Switch back to above and pull the switch. Now you can safely cross the chasm, provided you make a clean jump. Down below, I would recommend using the Knight and Hillbilly to recover the trinkets. You can ignite the flare, activate the Knight's special ability (or just RUN if you're not the knight), and sit there while the rocks explode in your face, taking NO damage. Use the Hillbilly if you're a slow swimmer. Honestly, you can complete the level with anyone though. Just swim fast and don't make any sidetrips. Dropping down to the next stage, be careful not to move too much while falling. You might hit the landing instead of the pool of water. Instant kill.....

2) Angry Miner
COD: Angry Miner, Getting crushed by floating plates, Not running from Dynamite

Other possibilities: Falling damage, Standing ON minecarts (keep it in the vehicle guys...)

Prevention:
You gotta have the bucket of water ready to catch that dynamite. THEN RUN LIKE MAD. It's best to use the knight for this. Even if you're holding the bucket n stuff, you can still protect yourself.
For the floating platforms (the puzzle with a train cart) be sure to place your characters off to the edge of the map, or on a stationary platform (NOT THE GROUND) it's easy to accidentally squish them when you're balancing out the platforms. Make clean jumps to avoid falling.

3) Zoo
COD: Getting shot by Zookeeper, poking crystal monster from the front or behind..

Other possibilities: Electrocution? Not entirely sure, but just go swimming when you're holding the tape recorder battery....

Prevention:
First of all I would like to say the "DEATH" in this stage does not count against the acheivement. It is just part of the story and unavoidable.
Do NOT approach the zookeeper. She will shoot you. Just charge up the recorder, record the angry cave monster and drop the recorder JUST BARELY within earshot of her. She should be at the EDGE of your screen. She be running!
Do NOT approach the monster at any time unless you are holding a hotdog. Don't let it get too close before you back up onto the bridge. Once it's on the bridge, it's gone.

4) Island
COD: Falling damage, Blast damage: explosive barrels

Other possibilities: Lava, sharks, drowning

Prevention:
Jump onto well - markes, solid objects only. Avoid deep water. Honestly, you don't have to touch it altogether.
Be careful when retreiving the pipe pieces to drop onto a platform or object nearby. It's easy to die from falling damage. Use the Monk if possible to avoid crevices altogether. You can directly get the parrot to rest on your shoulder using the special ability. Forget looking for crackers! Also use the Knight when handling the explosives: bring them all out to start a chain reaction. The furthest from you should be on the water drain. another should be a little closer to you. Finally, Light a barrel by dragging it near the lava. Change directions and push it down the hill! There's always your special ability if you need to use it.

5) Gift shop return
COD: Lava, drowning (in water)

Other possibilities: Falling damage

Prevention:
This is just like the first visit to the Shop, only NO Crystal Cave Monster and now there's..lava below. Be careful where you drop and land...Also you need to swim fast to recover one of the trinkets

Know your Causes of Death – Character-Specific Stages

I am not going to put these in order of where you find them because it really depends on which characters you bring. If you don't bring the character whose story is told on a certain stage, well, it's not going to be unlocked.
Certain combinations of characters will help these stages, but you are required to use the special ability (Q) of the character whose stage it is.

Knight
COD: Fire, sneaking up on the dragon without a distraction, falling damage, being shot with arrows by the guard(s), blast damage

Prevention:
Press Q while midair to start falling while being protected (will allow you to pass through fire). Be sure to open the gates for your alternate characters, you WILL need them. ONLY have the Knight stand in the elevator. As soon as an alternate flips the switch to lower you, switch back to the Knight and press Q. Leave him like that. Once he's right in front of the guard, have your alternate sneak behind him and steal the keys. DO NOT attempt to steal the keys unless the knight is ON THE ELEVATOR and right smack in front of the guard. Feel free to prove me wrong, but I've tried other things. They resulted in many painful deaths. Also, just send the Knight to do stuff like blasting out rocks with dynamite. Choose the torch(es) closest to the sword in the crypt. Jump right up underneath the sword, place the lit dynamite and press Q. You can bring the dynamite from any distance, but it must not be lit until you are at a good spot in the crypt.

Time-Traveller
COD: Being trampled by the dinosaur, dropping rocks on your teammates, taking falling damage, trying to take the gate key before you kill the caveman in the past

Prevention:
There's a certain distance you can stand from the dinosaur while having it stop right underneath a good spot to drop a rock AND avoid getting thrashed. FIND IT. Experiment with this a little.
Also, when you're on ladders, you can press the up or down button with or without the spacebar, and jump a ways down. If you CONTINUE to hold it from the top of the ladder, you will most likely die. The distance you fall is reset once you lift your finger from the spacebar, since this causes you to grip the ladder again. Always assume if there's a ladder, the distance is unreachable without it AND it's high enough you'll hurt yourself if you fall (which, again, is a OHKO).

Monk
COD: Falling damage, drowning

Prevention:
(Practice patience by using Shift to walk (instead of ending up running if you take about 3 or more steps in one direction).
Be careful when you get to the rug, this part is tricky. Otherwise, just don't be an idiot
Jump onto the rug in different order than is convenient. Monk gets on last, lightly tap the arrow to face whichever direction the "object of desire is" (or should be. Spoilers!). You don't want to see his knees and feet move because...well, you're supposed to stay still. If you move, the carpet will disappear when you get to the top and you will all fall from a great height and die.

Hillbilly
COD: Electrocution, Drowning, falling damage, falling off the ferris wheel

Prevention:
Switch back and forth between characters with good timing. You have a certain amount of time from when you turn off the generator with the wrench to collect the fuse box above the ferris wheel. Make sure to turn off the generator when the ferris wheel reaches the top of the screen, so you're not electrocuted when you jump off to collect the fuse. ONLY send the Hillbilly to go underwater and run errands, especially right at the start of the stage. You can press Q after you jump in the water, but make sure you don't leave him without an air bubble longer than a few seconds. Also, be careful on ladders and ropes that you don't jump sideways off one to move down quicker. You can die easily that way. Try and jump to the next nearest "cart" on the ferris wheel to avoid falling too far.

Scientist
COD: Shot by security guard, fried with jet blast, slipped off a ledge

Prevention:
Stay away from the rocket. The only reason you ever need to be down there is for the fuse. Grab it, use it, and head inside. The rest of the story takes place in the lab.
There is a container of sleeping gas...I don't think it kills your character, but it'll make them sleep for a bit. Switch the ventilation up above so the air flows OUT from below TO right above the security guard. Drop the sleeping gas there. Now that he's down, you can move about relatively freely. If you have the Monk in your party, use him to grab the hazard sign "slippery when wet." If not, just take baby steps toward it, or away from it - then snatch it up, or toss it to some flat part of the map, away from interactions you need to make to get through this stage. The security guard doesn't move an inch at any time, so don't bother trying to make him slip.

Twins
COD: Falling damage, smoke inhalation, steam burns

Prevention:
Extinguish the fire in the fireplace before descending. Take a bowl/pot, fill it up from the sink, and press E when you're holding it and at the rooftop, at the top of the chimney. Make nice, clean jumps when you need to move around the stage, and don't jump to move down a rope or ladder if the tip of the rope (or ladder) iis visible right now, on your screen. Make sure to turn the valves down below before trying to pass through any steam you see.

Adventurer
COD: Spikes......spikes, and more spikes. Getting squished by moving platforms and stuff

Prevention:
Have the adventurer make nice clean jumps, make good use of the grappling hook. Some of those traps/pressure plates can be avoided, the ones that make spikes close in on your other teammates. You can jump right over them, but be aware there's probably a spike pit just beyond that pressure plate. Practice moving mid-air if possible (don't kill yourself :P ).

Get to the top of the ladder after you exit the Giftshop for the last time. Once you pop out on top, you should see a little window pop up from Steam, saying, "Who wants to live forever?"
Congratulations!

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