Lately i've switched it up. I isolate first, then do a compound movement second. It's good for a change. example: standing alternate db curls. Then, standing barbell curls, and cheat the last couple of reps on your last set.
I usually started with bb curls, then preacher curls, then by the time i got to db curls, my biceps were too fatigued to use any serious weight. So now i'm doing the first routine i described for 4 weeks before going back to my old routine, but on the old routine, i think i'll start with bb curls, then go to db curls. I always finish with "Ronnie cable curls" for a great pump. These r done on a low cable with a cambered bar attached to it. Stand facing away from the cable station with the cable between your legs and grip the closer part of the cambered cable bar. When curling, don't lift your elbow's up or you'll brush the sack with the cable. Not comfortable. Before this exercise i forgot to throw in hammer curls, so i'll start bitching and moaning on the way out of the gym. But don't u forget to throw them in there. Hope this helps.