My chest blew the first 15 years of training, and it's only been the last 3 years that it's become a decent bodypart. What's helped me personally...
1)Proper alignment is the most important thing. Squeeze the shoulder blades together, stick out & flex your chest (without arching), and keep the elbows wide, with the hands slightly angled in holding the bar. I hear people say keeping the elbows wide can cause shoulder injuries, but many times I don't think they're talking from real world experience. I had shoulder pain BEFORE I started flaring my elbows. Now my shoulders never hurt, and I lift heavier than ever.
2)Lowering reps on chest work. For way too many years, I did chest work in the 6-10 rep range. Once I lowered reps to 3-5 with high sets (6-10), my chest finally grew.
Somebody mentioned isometrically pushing inward on the barbell. That's worked well for me too, especially on incline presses. 1 1/2 reps have been successful too, with the 1/2 rep being in the bottom.
Cable bench presses (X Presses), where you go wide at the bottom and cross the hands over at the top are effective, as well as DB presses with low pulleys attached to your forearms with cuffs. These look goofy, but they work well.
And as odd as this sounds, deadlifts have added thickness to my chest.
Hang in there and don't give up. Even if your chest is behind the rest of your body genetically, there's no reason you can't build an impressive chest.