Pop Destiny in all team fights. If there are any high priority targets on the enemy team you want to stay out of range and wait until the enemy commits then port in and kill stragglers. If the enemy team is stacked with bull**** build defensively, if you're better than the enemy build mejais and go balls out in AP/MR Pen.

Defense:

Rod of Ages
Merc Threads or Ninja Tabi
Mejai's
Banshee's
Guardian Angel
Rylai's

Teabagging Snowballing ez mode Build, this build assumes you're smarter than your opponent and can outmaneuver them:
Lichbane
Mejais
Sorc Boots
Nashor's Tooth
Void Staff
Guardian Angel