Here are my general strategy tips for AoB:
1. Use the luring technique to kill former humans, hell knights, and barons.
Carry around 5 pistols with you for this purpose. If you know some of the above are on the other side of a doorway, drop a pistol in front of the door, move to the side one square (so you will be outside of their vision when the door opens) and open the door. Wait until they come to fetch the pistol and stab them repeatedly.
If you find one of the above mentioned enemies in the open, drop a pistol where you are. Move backwards towards a doorway, dropping pistols as needed to continue the trail. Wait on the other side of the doorway until they show up and then stab them repeatedly.
It takes a little experience to figure out exactly how the enemy movement and vision works and there are some quirks with it, but it is generally straight forward.
2. Avoid death until you get the chainsaw. This means avoiding demons at almost all costs. Also avoid imps, and rooms with levers unless you can get them in close range.
3. For trait path, do Brute->Brute->Berserker->Berserker->Berserker.
Maxing berserker is very important. When you are berserk, your movement bonus allows you to close with enemies very quickly. After that, do Hellrunner, Ironman, more Brute, etc however you feel like. Usually I will do 1 level of Ironman first just to increase my survivability.
4. Don't take chances or get cocky when you get the chainsaw.
Even after you get the chainsaw, the game is hard. Continue to play it safe.
5. Use the running tactic to get places quicker. This can be for getting to a globe, getting away from an enemy (outrunning a demon), running to the stairs, etc. Running is your friend. Globes and medi-packs reset your status to cautious from tired, allowing you to run again.
6. Plan on dying A LOT.
No way around it. It takes a combination of good strategy and some good luck in level layout, medi-packs, globe placement, etc.
Hopefully this is helpful. With some practice you should start to see the chainsaw more and more often. Then eventually you will get a couple games where the stars are aligned and you survive to the Unholy Cathedral. Then the game becomes extremely fun. :)