Make a list, or if you're capable, a storyboard, of all the images / shots / takes you want to have. Then sort them in a way, that makes it convenient for you to record them, for example, you have a shot of a car hitting a body and a close up of a face, and the order in which they should appear in that short film is: car > face; but the order they appear in the game (bad example) is: face > car, you shot them that way (face > car).
As I don't know, and many others too, what your intro consists of, shoot it whenever it is convenient or edit it together with already existing footage you edited before.
As I, and others, also don't know where the sound comes from, I take a guess, that you record your own sound. Either record it after "filming" and have made a rough cut, or record it before filming to accommodate the shots you take.