Your best bet is probably to find a Best in Slot list for your class / spec. Items that are on the BiS list (even if it's only the raid finder version) would likely be good candidates. Sometimes it can be good to upgrade based on how hard it will be to find an upgrade. Weapons and trinkets are rarely a mistake to upgrade unless they are terrible fits for your class (e.g. a hunter who get a bow with tons of mastery might not upgrade it in hopes of finding a ranged weapon with crit / haste).