2 1/2 Foot Grow Box

So im working on a two and a half foot grow box out of a dresser, ive done just about everyting except put the clones in which im getting in a few hours. I have a quick question.

Whats the best way to go about getting the largest yield with the size box I have? Just keeping it trimmed often to keep the size down?

You'll have to flower before they get too large. No trimming is really necessary...you could top or something of that nature but hacking away at a plant because its too big to be contained in your box isn't the answer. Just flower at the right time.