I didn't see a guide like this so I decided to make one, but please note:

I have not gotten all the achievements.
If you have advice on how to get an achievement, I'd love to add it.

Thanks for looking!

*A note about difficulties* If you're playing on newcomer mode (ie the 'easiest' game mode-you have 6 health instead of 5), there are some achievements that you are unable to get. There doesn't seem to be a consensus on which ones those are, so if anyone knows for sure, please leave a comment!
Here are the ones that I think are locked:
'Contender' ie beat horde mode
'Bully' beat all bosses
'Masochist' since it's a NG+ achivement
'One shot' beating the game without dying
All the boss rush achievements
'Diamonds are forever' Collect all modules
'Shine bright' Collect all gearbits
And subsequently 'Hoarder' since collecting all the modules and gearbits is part of this one.

Edited 12/31/2017 to include new feedback I got in the comments.
Edited 6/11/2018 to fix the spelling of 'achievement' in the intro (yikes)

Nothing's Easy, Now is it?
Opening Death


Die in the very first area



I don't know if you can get this one throughout the whole tutorial level, or if getting murdered by monsters counts. I just jumped off the ledge until I died.


If you miss getting this one at the beginning of the game, you can get back to this area later. Thanks to Linebeckable for verifying that you can get the achivement later as well!
Here's how you get there:






Then just keep advancing, and bam.

Meditation
Casey would know what to do


Don't press anything, and wait until your character sits down.



Then don't move for ten minutes (I timed it, it's 10 minutes exactly).

Thanks to Gabriel for suppling this one!

Dummy
Trick a Dirk to jump off a ledge


These guys are Dirks


The easiest way (in my opinion) to get them to fall off is to stand right on the edge and get them to attack you.


Bye-bye!

It also happens a lot when you're fighting a bunch of them at once. Or if you're in a room where part of the floor falls away when you step on it.

Chain Dash Champion
How many can you get?


To get this achievemnt, you only have to get 25 chain dashes.



Which is fortunate, because I'm awful at it. If you're playing with a mouse and keyboard (like me) and are having a lot of trouble chaining dashes (like me), you can try changing dash to the Left Mouse Button. It made things a lot easier for me. You're probably not going to need to use your sword in areas where you need to chain dash a lot (such as this one), clicking rhythmically is easier than hitting the keyboard for some people, and you can just change it back when you're done.

Alternatively, in this particular case, and when you're trying to get to 800 dashes, you might find Dolo's idea really helpful.
http://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=659122851

Basically, instead of trying to click around the entire room, you can just put your mouse to one side and move back and forth by hitting one key.


Like this






That's how I ended up getting this one, actually.

Nice Shot!
Kill five enemies with a bomb.


Pretty self explanatory.

Buy bombs here


Then find a group of enemies and throw a bomb at them.



Yes, I only got three there, but you get the idea. The idea being to throw bombs where the enemies actually are, unlike my preferred method.


A good spot to get this one is to the South
Take this elevator


Down the stairs


Into the next room


And voila!



Thanks to rokcat and ForgottenCrowd for suggesting this spot, and rokcat again for giving directions.

Natural Leader
Tame a certain wild creature


*Note* This is one of the 'hidden' achievements (1/6)
As far as I can tell, you just need to stand next to one of the snails in game until the achievement unlocks. Don't try to touch it or else you'll squish it.

*Another Note* Apparently some people have trouble unlocking this one. I honestly can't remember how long I stood there to get it, so I'll just add a little warning that it could potentially take a couple of minutes.

Here are the locations of the snails I've found


To the East







In town






To the West

Diamonds are Forever
Collect all modules


What it says on the tin.

I reccomend Steeper's guide to find the ones you're missing
http://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=658199351

or Akyrl's guide

http://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=658874958

Shine Bright
Collect all Gearbits


These guys are gearbits


Cable has a really nice guide
http://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=665910741

After buying every single upgrade, if you have all the gearbits, you'll have 6 and a half total credits/monies.


Bug also posted a site that can read your save file and show you which ones you're missing, which is super awesome! It is really annoying to have to go through and check each gearbit off or try and remember which ones you've already gotten.

http://anishlr.github.io/HyperLightDrifterLocator/

Walk in Closet
Collect all outfits


Besides the clothes you start out with, there are 9 other outfits to find in the world. You can access them from the consoles in your house. Each outfit/sword/HUD has a different effect.



Again, Steeper's guide is good
http://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=658199351

or MageKing17's clothing guide, which also details what each outfit does.
http://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=659138683

You can call me Stretchy has a more detailed guide as well
http://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=659081549

Hoarder
Collect Everything


Collect all modules, keys, gear bits, tablets, guns, upgrades, and most of the outfits.


*Edit: Thanks to Llefty for supplying the things you don't need to get, which are the black outfit you get from beating the challenge rooms, and the New Game+ outfit.

One Shot
Finish the game without dying


Also self-explanatory. So simple, yet so difficult.

EDIT
I haven't cared enough to try for this achivement, but Ahn't May - Off to studies gave a way to do this that doesn't invovle having to start over every time you die. I'll just post what they said.

" 'One Shot' is a difficult achievement, but you can actually make it easier on yourself by cloning saves. Even if you don't intend to cheat by cloning the saves occasionally and then loading an older save whenever you die, cloning the saves to ensure you have one save at the very beginning of the game is still useful... Unless you like watching the unskippable intro movie over and over again (in which case, I strongly recommend a psychiatrist instead).
And let's be honest, the game loves missing inputs sometimes, and you swear you pressed that dash button before those crystal traps stabbed you through your poor feet, or that time when you reeeeeally needed to toss a grenade into a mob, but the Drifter was like 'nope, not doing it'.

If you want to look for the save files, go look under "C:\Users\[User name]\AppData\Local\HyperLightDrifter" (I dunno where it'll be located in a Mac, sorry). "

If you are a mac user, it might be either here ~/Library/Application Support or here ~/Library/Preferences . You probably know your computer better than I do (or just ask google).
Thanks for the tip! I didn't even consider doing this, but it would be super convenient not to have to watch the opening movie every time I just want to start playing.


Luke 'M4g1cW4rr10r' Has an alternate tactic you might employ, or use in conjuction with cloing saves. If you turn off your computer before the red death animation screen has ended, it won't register as a death and you can just load your game file. Not sure if alt-tabbing out and then closing the HLD application would work, but useful information none the less.

And to the dude that said this achivement isn't difficult, have you ever considered that maybe some people are garbage at recognizing patterns and always get squished by the moving blocks? Bet you didn't think about that.

Don't Give Up!
You can do it!


Die 1000 times.

Thanks to Gabriel for telling me about this one!

Since this achivement is such a pain to do legitimately, here's another guide that shows you an easy way to get this one that involves editing the save files. I haven't done it personally, but if definitely works.

https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=959972363

Star Athlete
Win at the sport of Drifters


*Note* This is one of the 'hidden' achievements. (2/6)

Beat the soccer game to the south of town. Thanks to everyone who commented confirming this one!







I used a strategy I saw a couple different guides recommending.



Basically, take out the bottom cylinder, then stand at an angle to the ball, aim your cursor at that bottom square, and dash diagonally into the ball. It doesn't have to be exact, and it should work enough times to get you the win. Poor kid won't know what hit him. (I say 'poor kid', but why do you go flying every time you make contact? Is this guy/girl shoving you every time? Not very sportsmanlike of them.)

The Dash Eternal
Perform the ultimate chain dash


*Note* This is one of the 'hidden' achievements (3/6)

Get 800 dashes in the chain dash room. Thanks to [F9] Nilth and Mettaray for verifying this one!

You can look at the 'Chain Dash Champion' section for a couple of tips on how you might get this one.

Contender
Beat Hoarde Mode



This is where the hoarde rooms are






As you can see, you need 12 keys to access it.

Like the name implies, you have to fight off hoardes of enemies in these rooms



There's one for each direction, and once you beat all those, you unlock another room where you fight a mixture of enemies from all areas.






Once you beat that one, you get a rad outfit and the achievement (I'm assuming)

Masochist
Beat NG+


Beat the game on New Game+ (which, just to be thorough, you unlock by beating the game once).

Librarian
Collect all tablets


These are the tablets




You can check your progress in this room




Which you can get to by going to the tutorial level, and then going past where you pass out the first time.




Check "Opening Death" if you don't know how to get back to the tutorial level.


*Note: Currently, you can't get this achievement retroactively, ie you either have to start a new file and find them all, or start from an earlier file where you might not have found them all.

Bully
Beat all bosses


Self-explanatory.

gbaker9000 Pointed out that you have to beat them all on one profile/playthrough. So if you're not getting it, that could be the problem.

Line Em' Up
Hit 4 enemies with one railgun shot


This guy is the railgun




Like "Nice Shot", find a place with a lot of enemies to line up, or a big crowd, and fire into it.
The spot I talked about in "Nice Shot" also works well for this one.

Armory
Collect all Weapons


What it says. I got this one retroactively by going to the menu and manually choosing a different weapon, but apparently that isn't fool-proof.

You get 4 of the 6 weapons by beating the main storyline, and the other two are found behind the challenge doors (the ones you need 8 modules for) for East and South I believe.

There are 3 boss rush achivements of varying difficulties (spoiler: they're all hard). You unlock boss rush by beating all bosses once (so it unlocks after you've beat the game once).

*Note* Steam considers these hidden achievements, so if you were wondering what the hidden achievements were, these account for 3 of them. (4-6/6)

Boss Rush Level 1
Beat Boss Rush with the Fully Loaded loadout

As the name implies, you have all your weapons at your disposal at this level.


Boss Rush Level 2
Complete Boss Rush with the Mid-Range loadout

You have 4 medkits, one grenade, reflect, chain dash, and an unupgraded pistol and shard gun (from the east 8-door)
Thanks Excaliboner P r i m e!


Boss Rush Level 3
Complete Boss Rush with the Naked loadout

Gonna assume you have just what you start the game with.

Confirmed by gbaker9000 that you just have the pistol here.