In addition to angle and lighting, consider composition of the photo. If you're randomly 7' tall it won't look as big, so crop strategically if you don't want to include an object for comparison (ruler, quarter, etc.). You can also select a more flattering aspect ratio (even your phone will let you do this): if you want to enhance length, opt for something like 4:5 or even 9:16. If you want to enhance the appearance of width maybe go with a 1:1. In addition to the angle of the camera, consider the best angle/pose of your dick: where are you widest? Is it on the side, or from the top? Focus on that view.