Most of my build experience is in putting together scrappers, stalkers, brutes, and blasters - but most of the stuff below applies just as well to most other ATs. ALSO SECOND BIG DISCLAIMER that most of my experience (as will become abundantly clear) is in building for survivability, mostly because my personal philosophy is that your personal survivability is probably the most important part of your character. So BIG DISCLAIMER that I'm by no means an expert, just someone who's trying to give a little bit of a primer for people completely new to IOs and putting together characters. I see these kinds of questions brought up a lot in help chat in-game, so I figured I would give kind of a basic idea here and compile a rough list of what IO sets give what bonuses, and a little advice and personal opinion on goals for putting together an IO build.