How do I decide what to build? I've been playing league for a long time, since season 3, and while my mechanics have gotten a little bit better I never know what to build. When I play champs like Kennen I know the core build I need like Zhonyas for teamfights and Lucidity boots for more flash/ults.

When I play a champ like Zed or Renekton I feel like their builds can be less cookie cutter depending on the situation, but I never know what I need because of so many different passives and actives plus stats.

How do I decide what to build? Do I concentrate on what the other team is building or focus on what their damage type is? How do I know what active item will be more useful per the situation? I've seen LL Stylish build phantom dancer or Triforce, is he just goofing around or what?
