As others have said keep your enemy at a distance. Learn to roll and shoot on the run. Whittle their health down a bit and then get in close for the kill. Also, depending on your level you will begin to unlock skills that will make combat easier.

My following strategy is for smaller machines. i.e. watchers.

One strategy I noticed early on is that the machines eagerness to attack you is an advantage for you rather than against if you know what to do because you know they will come straight at you full tilt. Learn the sounds and the subtle animations they make just before they attack. Once you have that down your inital step in most combat situations is going to be roll/evade the first attack and follow it up with a heavy hit. Then override or critical strike. Repeat. I rarely used the quick strike as it doesn't deal enough damage or incapacitate the enemy.

I try to override only when they are isolated as it leaves you open to attack during the animation.

Heavy attack note: learn how long it takes for that strike because it's a little slow.

Hope that helps. Good luck and happy hunting.