This guide is based on the Witch Hunt version 1.22.

You have to finish the game at least twice to get all the achievements. There are mutually exclusive achievements Atheist and Help from above, and you can't get Necronomicon in Perma mode because the Second Chance skill is not available there.

Use this guide's map to find everything: https://steamproxy.net/sharedfiles/filedetails/?id=2060713314
This map misses a few things, but everything achievement-related is there.

Get these skills early in the game:

• Lockpick master
  
• Skilled merchant
  
• Bounty hunter license

After acquiring Bounty hunter license you will get around 10 coins for every monster killed, with it you can obtain a lot of money just by walking around and killing respawning mobs. Then you can simply buy all skills and items sans glowing stone which you can grab for free from the spooky house in Bellville.

Finish game not using any silver crucifixes or watcher totems.
This makes finding and fighting bosses harder, but bosses do not regenerate their health while you can run away and make a save from time to time.

Don't get attacked by a whisperer.
If you hear a whispering sound don't approach it. Turn away or make a detour. If you've caught a screamer, exit and reenter the game.

Finish the game without dying.
Second chance skill will prevent death if you have 45 mana.
The game updates save file upon death. But you can still make backups of the save file from time to time and restore the latest one in case of death. Steam Cloud should be disabled when restoring backup. To save use mana stones or travel to Bellville.

Unlock 5 chests in one playthrough.
Game has a limited set of lockpicks and by default success rate is 35%. Upgrade this skill using Lockpick master first(success rate 65%), or there is a chance to miss this achievement if you're extremely unlucky.
There are 5 chests in the forest(check the map) and 2 in Bellville(barn and spooky house).

Attack the beast.

Kill the beast.
Better get all the regular achievements before killing the Beast because later stages have more nuisance.

Destroy the sacrificial tree.

Kill the witch.

Finish the game.
Kill the last boss.

Fire a cannon.

• Get Cannonball
  
• Find cannon and use it.

See the map guide.

Kill the night flier.
When you notice a large bat, shoot it with your musket. Get a book from its mouth for free. Better not shoot it when it's directly over the lake or you may miss getting its book(no big deal though).

Save a dog.
After entering the forest go right along the border. You'll need lockpicks to open the gate, better postpone this it until getting Lockpick master book.

Make 20 headshots in one playthrough.
Every headshot counts. Tree boss has a lot of health and can be easily headshoted enough times.

Kill 50 enemies in one playthrough.
Easy if you explore the whole map and then continue hunting.

Kill 5 deadblinds in one playthrough.
Deadblinds are red silhouettes which reddens your vision and hurt when see them for more than 2 seconds. Hide behind a tree or look into the ground, then shoot them with musket from afar or use your saber when near. Any hit will kill them.

Unlock and visit every location behind locked doors.

• Shack near the cabin
  
• Dog gate
  
• Bellville: Witch's house

You don't need to enter Necronomicon room.

Find all the save stones in the game.
One is in Bellville's graveyard. Check the map guide to find the rest of them or just explore. They're glowing and seen from afar. You don't need to use them, just approach until it's get marked on your map.

Unlock all skills in one playthrough.
With Bounty hunt license and enough exploration you'll get plenty of money and can buy everything. You can get 5 books for free - one from the Night Flier, one from the witch's house in Bellville(safe requires password from the spider cave), one is just lying around and the white ghost can lead you to it, two are in the chests. Every book is given randomly, one of those you don't yet have. Consider buying cheaper books first so you can get expensive books for free. If you got all the books already you'll receive 50 coints instead.

Find the weird looking skull.
Check the map.

Find the book of the dead.
Hint: Die in the Bellville when you have the Second chance skill. Don't forget that you need to have 45 mana or you'll really die.

Attack an enemy with lightning using a silver crucifix.
Crucifix attacks only boss monsters in the vicinity. Doesn't matter if you have the Wrath of nature upgrade.

Finish game in perma mode.
This is the hardest achievement. Game saves only several times: after entering forest for the first time, and after killing every next boss. There are four bosses in total. You can use unfair methods to kill them quickly, or properly hunt them. And you don't get the Second chance skill to prevent death.

Unfair way: check Witch Hunt speedruns on Youtube.
Hunter way: Hunt like a hunter would. My strategy was to find almost everything on the map and get most upgrades before killing the Beast. This took awhile but later I also had enough money to get around 20 crucifixes.

Learn to use saber. Start swinging before monster reaches you. Sidestep right before monster attacks you. I killed spiders quite easy mostly without receiving any damage at all by strafing around them. Crawlers are nastiest monsters, it's quite hard to hit them.

Learn boss patterns in normal mode.

Use crucifixes for Witch and Child only. It is imperative to get the Wrath of nature skill beforehand.