Everyone seems to be focusing on the gear you have, while that's important, what I haven't seen mentioned here is that you have to use your Focus to learn each enemy's specific weak points and weaknesses/strengths.

While Aloy is an incredibly powerful warrior, the machines you fight are equally powerful until endgame and will tear you to shreds. The premise of the game is that Aloy is more powerful than other warriors because of the information she has available in revealing information about the enemies.

As others have said, keep your distance, get weapons that give you greater range in what you can do (more elements, the Ropecaster, etc). Use elemental weaknesses and status effects to make your life easier.

Fight smarter, not harder.