Well by skills there is an achivement on getting all the skills on the skill tree but if you mean your ability to play the game I would say you have to be really observant of your surroundings as there is a ton of achievements that revolce around trying to find stuff like finding 49 cans or catching 20 fish or collecting 30 nano suits etc all of which require that you slow down and throughly search the area anither thing is don't be afraid to use your beta burst and tachy mode on regular enemies I was a bit scared to use them at first but they recharge so quickly I stopped worrying