My chest was always a weak point, but while it may never have looked like Ronnie Coleman's in his prime, I did manage to make noticeable improvements over time.
First, I want to stress a couple of things. First, that genetics are the ultimate determinant of what your chest can possibly look like. While you may never develop the physique of your dreams, I have no doubt that you (and everyone) can make some progress if they're smart about things - and somewhat realistic.
Secondly, regardless of all the variables you can play with, you will need to ensure that you are pressing (that is performing the movement) in a manner that optimally allows you to recruit your pecs. You can find many explanations of keeping your scapulae restracted, your delts from moving forward etc etc, but until you actually FEEL everything going through the motions, you won't be getting the most from the exercise.
Now, a few things that worked FOR ME over the years.
-Increased frequency during my off seasons. I would keep a lid on overall volume, but with 2 chest days every 6-7 workouts, you could really see the differences each time I stepped on stage.
-Not obsessing about pressing. I figured out early on that I could press some very respectable weights, but this was most likely due to my natural delt and tricep strength. Learning that you could build a very decent chest relying on many other movements is tough for people who grew up on old Flex magazines, or love screaming about how much weight they're moving, but swallowing your pride and being willing to try something else isn't done without some intelligent consideration.
-Limiting ROM. Playing into my strength curve, I found that eliminating the lock-out portions of certain chest movements, and instead focusing on getting a good stretch, and keeping tension on the target muscles paid dividends with my development.
-Being lean totally changes how your muscles look, I knew that when I was relatively lean (or even in contest shape) that my pecs would "square off". However, maybe genetics, maybe just my imagination, my pecs looks much more "puffy" most of the year. To look at the shape during an off season, and predict how much different they would look when dieted down, there's no way they even look like they belong to the same person. So for the many gym rats who write off their own chest shape when looking at their favorit heroes in magazines or online, don't despair, but realize how much bf levels can seriously alter how everything appears.