Caddis hatches progress upstream daily, therefore; being on the leading edge of the hatch can often make or break your success. If the trout have been feeding heavily on caddisflies for a day or two, they will be stuffed and unwilling to take your artificial, no matter how well your fly is presented, or how many naturals are on the water!
Similar to midges, caddisflies pass through complete metamorphosis. Their lifecycle consists of four stages: egg, larva, pupa, and adult. All phases can be important as far as fly selection is concerned, but to date; I have caught more fish on pupae imitations than anything else. I still recommend carrying a thorough selection of larvae and adults because you'll need them. I would also suggest stocking your fly box with a few egg-laying adults too, as they are productive during the evening hours when the females come back to deposit their eggs.
Caddis pupae can be dead-drifted or allowed to swing in the current. When a fish grabs a pupae on the swing it is one of the most aggressive strikes you'll encounter with a nymphing rig. I typically fish a pupae off a larva pattern to cover my bases. Don't rule of wet flies ether as they can be extremely productive during the height of a caddis emergence.