The magical word is "cheese". I'll keep it short with following Examples:
- most of the bigger Bosses are pretty easy if you try and stay right below their ass. First boss, the Cleric Beast is the best example. Dark Souls Wolf Boss "Sif" teaches you this tactic.
- Dot and run/hide with poison knifes works like a charm just like it did with poison cloud or poison arrows in older Souls games. Hit the mob a cpl. times till the poison damage starts ticking and then run and hide somewhere you can't be hit. Rinse repeat.
- Use the environment, some mobs can be staggered off a cliff or ledges by using the gun repeatedly. The Machine Gun asshole at the village is a very hard fight unless you run up the ladder and shoot his ass 3-4 times till he falls off the tower. Make sure to reload the game up there in order to get the loot, it will spawn right at the edge. In older Souls games you could use Kick or Shield Stun for the same effect.
- Use the environment and hit through objects or walls. For example the werewolves can be lured down the stairs to the dark building, they get stuck at the doorframe and you can get hits in free of harm. Or 2nd Boss Father Gascoigne: Keep a tree or gravestones between you and the Boss and use long range weapon/attacks relatively stress free. Or run him around large objects, wind up an attack before he comes around the corner.
- Farm blood for molotov coctails. Together with a oil urn these are pretty powerful early in the game and quite cheap.
- etc. be creative, use the map layout / environment, think outside the box and use the items the game provides you with.
- play co-op, 2-3 players make every encounter pretty trivial
- don't hate (the cheese, embrace it). Souls games hate you, you are only using the tools given to you. You will still die tons, but you can try to beat bosses yourself without having to watch lame ass lets-play videos on youtube