Pocket shines in Mid to Late game
In mid game you do a lot of damage from your spells - cloak + satchel do 300+ damage together, multiple procasts with some gun shots in between will lead you to many kills
During this time you should roam - generally move around the map to do things, usually grouping up with your team to gank someone
In late game, when 300 damage isn't as scary, transition to be more ult heavy
Gameplan is - Majestic leap, Barrage, Dive, Ult, throw Decay at someone, Get out with Cloak + Satchel (preferably while doing damage with these two spells to proc Spirit Burn)
Wait for Affliction to tick down, then go back in to finish off enemies