Know the way the character stands, walks, and poses. If you are the kind of cosplayer that goes in character at cons [like me], then this knowledge really helps sell it.
For example, my Bane cosplay. Bane is a special case because so much of his face is obstucted, that even in the film, the actor was forced to rely on usage of the eyes and body posture to convey a certain feel for the character. As a cosplayer, I will be doing the same. It is the small things that will really sell it.
How Bane not only has his hands perched on the straps of his flak jacket, but he walks with a slight swagger, his had bobbing slightly, like he has no f*cks to give. Getting that slight droop in and tightness in the eyes, the right pacing of walking, etc. Angling and cropping is in the hands of the photographer, as they have the camera. There is no reason why they cannot maneuver around you to get the pic they want, but you need to be able to convey the life of the character through your pose, expression, and physical attitude.
tl;dr - get deep in character and you will start to move like them and eventually pose like them. Failing that, just study the character to the point of perversion.
Captain Jack Harkness: 5%
Booker Dweitt: 5%