Photoshop Graphics

i'm not new to the photoshop world, i've been doin' it a while. i've done quite a few rides and you can see some of them on my profile. but my biggest beef is with the graphics. i've really been workin' hard the past few weeks to figure it out myself. i can get all the angle right and get it to fit, but how can i get the shadows and highlights onto the graphics that make them look like they form with the body line of the rides and not a flat pic standing next to them. thanks for any help that i can get.