A: Generally, pedals that do gain (boosts) or dynamics (compressors) processing; EQs, filters and filter-type pedals (wahs); and overdrives and distortions go in front of the amp. Most players put time-domain stompboxes and processing in the loop. This includes delays, chorus, reverb, and so on.
And, as always, there are no rules. Try your pedals and processors in both locations and in different orders. Whatever sounds good is good!