I don't seem to be able to avoid shooting all monsters. In the beginning, you are taught the trick with the rotting meat and the space in the wall where you can hide, but it's the only place in the game with such a space to hide! I'm in the basement level at the moment and there are too many monsters wherever I go—I just don't have that much ammo. I read it's even possible to finish the game without killing any monster, but I don't see how you can avoid them if you can only walk to the left/right.
No hiding spaces? No bullets? No problem. Use a flare. All the nearby monsters will panic and you can just walk right past. Here's a video demonstration.