All achievements divided in two large groups:

1. achievements you likely get during campaign walkthrouhg (paragraph 1);
   
   
2. achievements that require some special approach, patience and free time to waste
   (paragraph 2)

Apart from that, there's a complete walkthrough (Impossible Difficulty) made by ^FuN^ DreeMax (paragraph 3).

If you are looking for a particular achievement, then press Ctrl+F and use popped up "window" for a fast search by typing achievement's name.

Achievements mentioned in paragraph 1 usually shouldn't require anything besides completing level by level and going through the campaign.

If there's anything deserves to be pointed out about the particular achievement, then details are given below the achievement's description.

Undertaker
Kill 400 enemies


Lead for Dead
Kill 1000 enemies


Moonshine Massacre
Kill 2000 enemies

Pretty simple: all these are for killing zombies.
Any difficulty is applicable except, maybe, "Easy" - I'm not sure there will be enough hostiles for the "Moonshine Massacre" achievement.

Popcorn Maker
50 headshots

Not consecutvely, in total - a piece of cake when you get magnum.

Mafiapocalypse
5 multi-enemy grenade kills


Spicy Meatball Mayhem
10 multi-enemy grenade kills

"Multi-enemy" means that there's a bunch of more than 5 zombies, usually, before some obstacle they can't overcome. Vinnie always makes a comment after multi-kill - so, you can understand if it was performed or not.

Cannoli Enthusiast
Eat 10 Cannoli

There's a pack of cannoli right after each checkpoint, usually, there're at least 2 checkpoints per level. So, highly likely, you will get it long before 1/3 of the game is completed.


Mechanic Maniac
Destroy 10 cars

On some levels no cars can be found, on others - at least few of them. If you play on "Hard" or "Impossible" mode, game itself will make you to explode the cars to kill as many emenies as possible. On other difficulty do not forget to destroy them on purpose.

Sonny Goes South
For killing 1st "boss"


Verminator
For killing 2nd "boss"

For further details do not hesitate to check paragraph 3 - complete walkthrough on Impossible Difficulty made by ^FuN^ DreeMax.

Boyscout
Complete the game on easy mode


Goodfella
Complete the game on normal mode


Godfather
Complete the game on hard mode


Capo Di tutti Capi
Complete the game on impossible mode

Generally, it works like that: for completing the game on higher difficulty achievements for lower difficulty unlock themselves automatically. For instance, completing the game on "Normal" difficulty gives you "Goodfella" achievement along with "Boyscout".

According to that, completing the game on Impossible difficulty should guarantee all 4 achievements at once.

Playing on Easy is practically meaningless - no tension, no interest.
Normal mode is a liitle bit harder, but still not able to provide a challenge.
Hard mode is controversial: on the one hand - perfect compromise between challenge and fun you get from playing, on the other hand, better to choose Impossible mode because in this case you will get 4 achievements at once.
Impossible mode - well, obviously difficult. Do not hurry, destroy every enemies 'wave' thoroughly before going further. Pay attention to boses' patterns - then it will be easier to beat them.

For details do not hesitate to check paragraph 3 - complete walkthrough on Impossible Difficulty made by ^FuN^ DreeMax.



If due to some reason you can't manage the impossible difficulty, then Postal Zombie's advice may come in handy; yet, you have to drop a sweat here too (at least a little bit):

To get all four achievements at once you don't need to walk through the whole level on Impossible difficulty. You just start and go on Easy and, at the end of the level, you switch the difficulty to Impossible and finish current level. Repeat for each and everyone of them.

Achievements pointed out in paragraph 2 require special approach: either completing level in certain way or performing special attitude.
Details are given below for each achievement.

WARNING:
To reduce time consumption required for these achievements, it's better to choose Easy difficulty (except "Live And Let Die" achievement).

Unfortunately, game saves your progress (incl. difficulty info) after each level. Thus, if you change difficulty for any of these achievements, you may have to complete particular level one more time on your "main" difficulty to "cover" the checkmark of that difficulty.

Therefore, I'd advise you to care about obtaining all these achievements after completing the game on chosen difficulty, unless you started with Easy by default.

Consecutively kill 25 enemies with a headshot
(after completing the game on chosen difficulty unless you started on Easy)

There're two ways to get this achievement:

• on later stages with Magnum and at least 25 bullets for it (so, you need to save them and that's not easy);
  
• on the very first level (The Ship) with your default gun.

In my opinion, 2nd way is easier, but has its own trick, though: you mustn't put away your finger from the trigger button while you are shooting at the zombie, otherwise, there will be not enough "power" to perform headshot.

So, reload your gun in pauses between fights, do not hesitate to run away when it's needed.

Be sure that you can overjump the oil burell right after destroyed stair - otherwise zombies start punching you and the burrel, that will cause an explosion and chain of consecutive kills will be broken (see the video below).

https://www.youtube.com/watch?v=wutdsqSY6lk

There's one more way to obtaine this achievement offered by Moon The Mischievous:

I think I've found an easier way to get the "Undead Head Harvester" achievement.

When you first enter the sewers fighting against the rats....

I went into the sewers and was shooting each one with the tommy gun. Went to the end, jumped up the pipes and hit the switch and went back along the way I'd come. Before I'd even got to the new area I unlocked the achievement - just by tommy gunning rats. I wasn't even trying for it!

Kill 20 enemies in the alleystreets, during one run, by kicking them into fire
(after completing the game on chosen difficulty unless you started on Easy)

You need "The Back Alleys" level for that achievement. It's not necessarily to kill every enemy by kicking them into fire - you need 20 in total.
So, you kill every enemy with guns untill the zone with fire, after that you kick them into fire. It's easy enough to have about 25 "victims" before the 1st checkpoint (see the video below).

https://www.youtube.com/watch?v=laUK0JTvB-Y

Complete 'Bonnino's Stripclub' without dying once on Normal Mode
(after completing the game on chosen difficulty unless you started on Normal)

Well, do not hurry - thoroughly destroy each zombie "wave" before running further. The most difficult part - not the level itself, but boss fight in the end (see video below).

https://www.youtube.com/watch?v=UxQuYe4tVnk

Survive the army stronghold without killing any enemies
(after completing the game on chosen difficulty unless you started on Easy)

The most time consuming achievement: level itself rather large, it's difficult to run through all of it - you need to have your AI partner make some killings and this ♥♥♥♥♥♥♥♥♥♥♥♥ is the stupid one.
It might be wise to get this achievement in 2 runs:

1. get to the checkpoint which is before bridge pillar (8:29) - it's ok to die on the way between checkpoints, it reduces amount of zombies chasing you;
   
2. take some rest and then get to the top (see the video below)

https://www.youtube.com/watch?v=nEyDTlo1IcQ

Survive the river level using only your magnum
(after completing the game on chosen difficulty unless you started on Easy)

On The River level choose magnum from the beginning and start running (literally) - there's no point to kill each and every zombie you see (you don't have enough bullets anyway).
Your main target - reach the next checkpoint.

Also, keep in mind that you must have at least one bullet for magnum available by the end of the level - otherwise achievement won't pop up (see the the video below).

https://www.youtube.com/watch?v=_t2hDSOHoEE

Survive the sewer using only your Lupara
(after completing the game on chosen difficulty unless you started on Easy)

On "The Sewer" level choose sawed-off gun (Lupara) from the beginning and be sure you have at least 12 bullets for it.
Kill enemies in economy mode: few with one bullet until you get to the surface. Do not hesitate to kick them to death if possible.

Then just run (literally) through the level - from checkpoint to checkpoint.
It's ok to die, it even reduces the amount of the enemies chasing you.

Also, keep in mind that you must have at least one bullet for Lupara available by the end of the level - otherwise achievement won't pop up (see the video below).

https://www.youtube.com/watch?v=WBHPWznZY90

Survive The construction site without killing any enemies with weapons
(after completing the game on chosen difficulty unless you started on Easy)

Rather difficult, even on easy - you need to be very accurate with jumps (especially in lift towers), avoid enemies because they won't allow you jump high, always be carefull with gansters who has Lupara or shotguns - its bullets usually throw you back right into the enemies crowd where you will be torn apart (see the video below).

https://www.youtube.com/watch?v=A0eQxJspH9o

引用自 ^FuN^ DreeMax：

My self-made challenges are here too and I'm pretty proud of them: defeat Mickey with only pistol and, of course, defeat last boss on 1st try without loading saves.
While editing video I noticed couple of weapons and hidden places I missed, but I used pistol most of the time (economy mode lol).

P.S. I hope you will like this video and enjoy it! Who knows maybe this even helps some1 to finish impossible difficulty ;)

http://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1116967562

• Intro - 0:03

1. The Ship - 2:17
   
2. Thugtown Hurbor - 9:44
   
3. The Outskrits - 21:41
   
4. The Back Alleys - 30:44
   
5. Bonnino's Stripclub - 52:25 (incl. Boss Sonny The ♥♥♥♥ - 1:05:06)
   
6. Army Stronghold - 1:07:58
   
7. The River - 1:31:38
   
8. The Sewer - 1:40:33
   
9. The Reservoir - 1:51:27 (incl. Boss: Mickey The Mutant Rat, only pistol - 1:54:42)
   
10. Secret Lab - 2:05:34
    
11. The Construction Site - 2:15:52
    
12. Rooftops - 2:36:51 , Last Boss Frankie The Fly (1st try, all 3 stages) - 2:57:03

That's all folks! Thank you for reading. Please, do not forget to "thumbs up" (it's on the top of the page, right below the description) if you consider this guide helpful.