learn how to contract your pecs and focus on doing that, forget about the weight involved. slow on the negative, like at least 3 full seconds, and the powerful on the positive. SQUUEEEZZZE the muscle at peak contraction. do a few different exercises. warm up sets are done in the same fashion as i just described, but only do a few reps with a light weight.  then jump right into your heavy set. aim for 8-12 reps.  stop one rep before hitting failure. just do one good set per exercise.  hit the upper, middle, and lower portion. so three exerices, 3 work sets, is good.  leave the gym with gas left in the tank but a tight, pumped, stimulated chest. hit the muscle again in 3-5 days.  -from personal experience