A very important thing what you have to keep in mind, is that how much time do you spent under tension. This is the process which starts the growing of the muscles. You have to associate your sets with the time under tension, to get better result and bigger mass of muscles. Many athletes do the repetition of the sets too fast, and they don’t wait to be under bigger tension, this leads to a reduced muscle growing, simply this is a wrong thing to do. You have to do slowly the repetitions to be under tension.
To obtain better looking pectorals you have to work in a kind of position in which your pectorals do the most of the lifting. Increasing the weights you do a harder workout, you put more force on your pectorals.