Well i've only just started learning theory so i'm not qualified to instruct you but at the moment i just mess around with chords till i find a progression that sounds good, i dont worry about what key it is in (at least not untill i gotta find the relevant scales so solo over them!) or whether they're dominant, sub dominant or tonic chords, i just let my ear be the guide, bit slap happy i know!, but till i learn more theory i just experiment :o