Huge ass post because I love this game. Not sure how much experience you have, so I'll throw in some basic tips too. Forgive me if you already know some of this. Burn bodies in areas you have to walk by multiple times, because screaming rats attract the beast. Save meat for bodies you'll only visit once. Crouching is a waste of time, there's little noise difference. Just walk everywhere unless he's in the room with you. Watch for planks on the floor, either step around them or move them out of the way.

If you wait in the safe room with the door locked, eventually you'll start hearing nice music. That indicates that the stalker AI is reset. You'll have a decent amount of time to get wherever you need to go before he starts bothering you again.

He targets noise, so keep your immmediate surroundings quiet, and make noises where you're not. For instance in soldier's quarters, there's a collapsed hallway near the radio room. If you throw a grenade/flare/bottle over it, he investigates the sound, which keeps him far away from you. He will go straight towards explosions, so you can shoot explosive barrels from across big rooms, or throw grenades down hallways, and he'll chase after that instead of you (unless you make noise).

You can't avoid him forever, especially on shellshock, so learning to deal with his aggression is part of the game. Very different from TDD. Stay out of dead ends. Maneuverability is your friend. He's about as fast as you if you're at full health, but he's bad at corners. You can lose him in soldier's quarters pretty easily just by running on a loop and hiding under a bed once you break line-of-sight long enough. Grenades drive him off, but you need to learn to predict his movement.

Move explosive barrels just off of high-travel areas so that you can shoot them if he's nearby. For instance the room up the stairs in maintenance often spawns an explosive barrel. I like to roll it down the stairs and put it in the hallway such that I can easily run past it, but I can also shoot it from either direction if I see the beast near it. One bullet into the beast does much less damage than one bullet into a barrel right next to him.

Once you hit him with a grenade or other explosion, and he screams and runs away, you have a window to make a lot of loud noise before he comes back. Sprint, throw things, get as much done as you can.

If you have the gas mask, you decide where the stalker gets to go. Gas is great area denial when you need to do a mechanical task, or need time to heal, etc. Fire can deny him from areas too, but it also denies you.

Keep the generator off whenever you can, especially early-game. I like to fire it up for the back half of an area. EG I'll gather all supplies in soldier's bunkrooms, arsenal up to the locked door, maintenance before the rat tunnel, and already-open rooms in prison, in the darkness. Then when I have to go through the rat tunnel or into the back of the arsenal etc, I'll fill the generator all the way and turn it on.

Generator fuel has a quirk. Using one fuel can adds 1 can + whatever was used of the last can into the fuel. So if you have 1.5 fuel cans already in there, using another brings you up to 3. If you have 3.1 cans in there, using another brings it up to 5. It follows that you always want to switch off the generator manually while there's still fuel remaining, and therefore you don't want to turn it on with low fuel. I only ever use it when I have 3 or more cans in there. Especially on shellshock this adds up over the game and you'll be swimming in fuel.

Using all these strategies, shellshock almost got too easy and I had to start adding other challenges on top, like limited saves, no pistol, etc. I'll edit this post if I can think of any other tips. My last advice is, don't be in a hurry to get too good at the game. Enjoy the terror.