There is no "right answer". Every writer does it the way that works, and often that means the way it works for this particular project. Movies are commonly made piecemeal, for a variety of practical reasons, with scenes shot entirely out of final sequence, and often the actors don't even know what the final product is going to look like. Good actors deal with this reality. The Pianist, which won big Oscars three or four years ago, was filmed essentially in reverse order, because its star (Adrian Brody, who won a Best Actor Award) needed to lose a lot of weight during the course of the story. They had him lose the weight first, shot the final scenes first, and worked backwards from there, to allow him to gain back the weight and strength needed for the earlier scenes.
Good writers don't worry overmuch about writing order, either. For some (Terry Brooks), it works best to pre-plan extensively and write-by-number thereafter. For others (John Saul), seat-of-the-pants is the way to go.
caw