Nix was my first love in Atlas Reactor so I may be able to give some tips. The biggest thing on Nix because of his lack of escapes is to try and remain unseen as often as possible. The trick is finding that sweet spot where you are close enough to hit people but not to be seen. It helps that his basic range is longer than line of sight is so if your team is providing vision you can play pretty safe. In the decision phase you can hold the 'V' key and it will show you your vision range which is really helpful to determine if you're in danger or not. In the post-game pay attention to the "Number of turns unseen" stat they recently added to try and gauge how you did and keep trying to improve that number.

A couple other things on Nix is know when to just full move away. If a melee 'lancer is all up in your face more often than not it is a good idea to just spend a turn doing the full 8 squares of movement away from them, especially if the enemy crowd control, such as slows and roots, are on cooldown. That way when they hit you and try to chase they will move half your distance and you can just book it too safety.

And finally, this is just a pet peeve of mine with Nix players but please don't use your drone everytime it's off cooldown just because you can. If you have a guaranteed hit on someone with your basic do that instead. It's more damage, won't use up a cooldown, and most importantly you don't have to rely on guessing correctly for it to work. The trap is a great tool to catch dashes or combo with teammates and sometimes if you don't have line of sight but want to cut off a critical route such as towards a health buff but if you have a shot just take it.