How to set up my P.A. that I own--how would you do it with what I got?

I am having some troubles setting this up. My monitors either arnt loud enough or feed back. What I have for main speakers is a pair of JBL's two fifteens and a horn. A pair of 15" 2 way PV Speakers for monitors, a pair of 18" black widow subs. A crown XTI series-1000 power amp and a crown XLS series-330 power amp and a Behringer 32 channel mixer model #SL3242FX-Pro. How would you hook this up for the best sound? We just play in local area bars and fairs.