Consume 6 small meals/day, low fat, moderate carbs and high protein. Drink plenty of water.
Workout 4x/week for 1 hour, finishing up with 30-40 minutes of cardio (stairmaster, cycle, treadmill, etc)
Pre-exhaust your chest by performing heavy flys, and dumbell pullovers, then focus on the benchpress. Rotate wide grip dips on the V bar with benchpress every two weeks to keep the muscles guessing.
For mass, reverse pyramids work best. After a brief light warmup, move to your heaviest weight first, then decrease the weight by 10% each set. Rest no longer than 1 minute between sets. (helps emulsify bodyfat).
After 12 weeks you should see noticable improvement in your mass of your pectorals, as well as a nice decrease in bodyfat percentage.