Since you're aiming to get all achievements, you need to be aware of the specifics of Conquest.

All achievements must be unlocked on one save file.

They aren't carried over several playthroughs, you have to do everything within one save file. This means that above else, you must ignore all achievements until you get Death and Famine, which you can't exactly postpone for later because they're in-one-sitting kind of achievements.

After you get those, you're free to go for whatever achievements in any order, as the levels are replayable at any time.

With that out of the way...

Right, so, let's start with these two bad boys.

They're listed together because the conditions for them are similar, and besides, if you're going for Conquest, you're gonna need both at the same time anyway.
The important thing here is learning the consistent routes that hit the sweet spot between relatively safe and fast. Deaths in this game by far waste the most of your time, so if you haven't died, you're probably on a good pace anyway. Speedruns can also be a good place to look.

Mind the very crucial part in the achievement description: "without qutting". This means without quitting to the main menu, and thus, exiting a current save file. You can Quit Mission at any time should you choose a wrong one or be on the verge of dying.(you can even be killed and still use Quit Mission just before you restart, and it won't count as a death!)

If you want a guide to follow along to, I've recorded my own routes here: https://www.youtube.com/watch?v=v3MKiHMKJnY

Self-explanatory, can be done on any level, but save yourself some time and do it on an easy one like Noisy Neighbors.

Can be done on any level with any melee weapon, but if we're doing this chronologically and without buying anything...
Play New High, use the hammer there to kill a bouncer.

Since you've done Pugilist on New High, wipe out the rest of the level with that same hammer.
Otherwise, can be done on any level with any weapon.

Blow up an undead on a toilet.
Can be done on either Smoke Signals or Lux in Tenebris, or any level where you can find an undead sitting on a toilet.

Can be done at any time, Charon's docks open after New High.

Sawn-off Shotgun will be your best friend here.

You can always come back to this level with more powerful late-game weaponry to get this achievement, but here's a safe strategy just in case.

While the patrolling zombies have their backs turned to you, stealthily make your way through the vents to a Shotgun lying on the bathroom floor.



After that, go wild. A single point-blank shot is enough to kill Bouncers, Punks and Puff himself. Bouncers should provide enough shotgun ammo, and you've got a .32 Revolver for backup.

The important thing here is avoiding being seen. You can be the loudest son of a gun and attract the entirety of the map to your position (not via a camera though), as long as no zombie actually saw you (also indicated by a red exclamation mark, though sometimes an orange one can pop up but anyway it's easy to indicate whether you've been seen or not).

You can be seen by the cameras briefly, so long as they don't shout.

Can be done on any level, easiest to do with one-shot weapons that allow bodyshots, such as shotguns or a Revenant.

This one is all about speed. Relatively, anyway. The bartenders take a really long time to be revived, so depending on how bold you are this one might not be troublesome at all. Point being, just rush into the level and spam your bullets like a madman.
The 10mm pistol that's available in the level is especially useful because its wall penetrating properties allow you to destroy the Bartenders' phylacteries without even needing to enter the rooms they're situated in.

Open the vents on both sides before killing each of them to quickly get around the level.

In Layman's terms, kill the melee sister with a melee weapon and the gun-wielding sister with a gun.

Same method as with Acrobat, Sergeants (the dudes with sledgehammers) can be 1-shot with either a point-blank sawn-off or a Revenant headshot. Pick a powerful weapon and let them get just close enough.

Just shoot the body as it's being revived, without killing the General. Easiest on Horror Show. Any weapon with a large ammo pool and enough damage works.

Kill the first sergeant with all the mounted sawn-offs, avoid all the grunts (or blow them up), clear the mines, bait the second sergeant downstairs and proceed safely to blowing up Timur. Exit the level.

Mind the achievement description - you need to clear Vall's nest, AKA the part of the mission where you're looking at a level through the rifle scope.

Get to the sniper rifle by any means necessary (again, bodyshots are okay for now), and after that go for nothing but headshots - indicated by the demons' heads bursting into flames. Don't forget about the bullet travel time and Reaper's flimsy arms not being able to hold the rifle steady. You are allowed to miss, just don't kill anyone with a bodyshot. Killing Vall ends the section, so clear the sniper nest of all the other enemies before killing Vall herself. Don't forget to do it with a headshot.

There's 21 enemies total, excluding Vall:

• 3 on the first floor
  
• 4 on the second floor
  
• 2 on the third floor
  
• 7 on the fourth floor, the one where Vall is
  
• 5 on the roof

Vall's head hitbox covers the rightmost portion of her head (drawn in green):

The achievement description only mentions the Ibzan level, nothing about Home Sweet Home.
Despite what the objective tells you, you don't have to kill everyone in the level, you just need to get to the portal and go through it without being seen. Stick to the shadows and don't forget about the sniper support!

There is now a Stars Calculator to help you out! Check it out here:
https://deadbolt.codemuffin.com/stars-calculator

There are two basic principles to getting 5 stars on a level:

• Rating depends on speed and accuracy.
  
• Rating isn't affected by the total time spent completing the level, only the successful attempt counts.

Basically, you can die on a level as many times as you want, so long as your last attempt (with getting into the car and whatnot) is speedy and has good accuracy.

Timur The Tinkerer is the hardest level to get 5 stars on - you only get shotguns as dropped weapons, and those naturally have terrible accuracy, let alone headshot accuracy. Landmines count as valid shooting targets, just don't shoot them with a shotgun.

Just collect all cassettes. For boss cassettes, just restart the level until they drop one upon being killed.

• Madam Stella drops her cassette even when she can get revived by the phylacteries - so let her get revived and keep killing her.
  
• Ibzan drops his cassette only in the "kneeling in the snow outside the mansion" state.
  
• Cassette drops have a 5% chance, except Roland & Ibzan who have 25%.

Here's a quick list of who drops what, and the best levels to grind the cassettes at:

• Zombie #1 — Punks, the zombies with baseball caps and 9mm pistols.
  Best Level: Smoke Signals (toilet on the left)
  
• Zombie #2 — Bouncer, the chubby zombies with sawn-off shotguns.
  Best Level: No Vacancy
  
• Zombie #3 — Roland.
  Best Level: Roland
  
• Vampire #1 — Succubi, the female vamps with knives.
  Best Level: Night Out
  
• Vampire #2 — Nightcrawlers, bats with suppressed PDWs.
  Best Level: A Lot To Give
  
• Vampire #3 — Madam Stela (as mentioned above, can drop after any "death").
  Best Level: Madam Stela
  
• Skeleton #1 — Grunts, the skeletons with automatic/"old world" rifles.
  Best Level: Horror Show
  
• Skeleton #2 — Generals, the tall skeletons who revive others.
  Best Level: Horror Show
  
• Skeleton #3 — Ibzan (as mentioned above, only drops after the final death in the snow).
  Best Level: Home Sweet Home
  
• Demon #1 — Cardinals, the demons with bats.
  Best Level: Drive Thru