Focus on contracting your chest and squeezing it as hard as possible during every rep. During both presses and flyes.
Alternate DB and BB movements every now and then. i like to do one BB movement and one DB movement for every chest workout.
agreed, and I'd focus on incline press as your main exercise by putting it first in the routine. Most people have good lower pecs. I've never seen anyone with underdeveloped lower pecs really, but lots of people have underdeveloped upper pecs and it's pretty much impossible to have the upper pecs "too big" really. That's my opinion anyways.
Here's a sample routine.
Incline BB Press: 4x5-10
Flat Bench DB Press: 4x6-12
Cable Crossover: 4x8-15
On Cable Crossovers, the higher rep range doesn't mean pick a weight that's easy though. I see lots of people doing them for 10 reps with a weight they could really get 15 reps with or doing 15 reps with a weight they could really do 20+ reps with. Pick a weight that is challenging.
By using this type of workout with the different rep ranges, you hit the fast-twitch muscle fibers at the start of the workout when you're fresh and strongest, and the slow-twitch muscle fibers more at the end and just focusing mainly on squeezing each rep as hard as you can on the last exercise. Also, might wanna do the presses explosively on the positive but with a controlled negative.