Pre-Production > Production > Post-Production
What is this math you speak of? Well, let me put it this way: anything you don't take care of in pre-production gets pushed to production, and anything you don't take care of in production gets pushed to post-production. And I'll give you three guesses on the biggest mistake a lot of filmmakers make, both amateur and professional:
THEY DON'T PLAN AHEAD.
Sounds easy, right? Hell, I thought so too. But it isn't. I would leave things undone assuming I had time to fix them down the road. Unfortunately, moviemaking by it's nature is filled with unexpected hiccups, so if you leave things for later, you often get left with you pants down.
My best example of this phenomena was Matt and I's short film Background(ed). Honestly, thanks to the help I got along the way, it went amazingly well through production. We had a great crew and script, and shot the whole thing over a long weekend. Of course, things got a little more difficult once we hit post. You see, that was the one phase of production I didn't plan for ahead of time. I didn't lay the necessary foundation for crucial things like sound editing, etc. Needless to say, the post-production phase of Background(ed) wasn't completed over a long weekend.
The good news is we still finished the film, and I learned a whole lot about how much stuff I had to take care before production even began. I highly recommend covering your bases all the way through post-production if you want to make your life a little more sane (and more importantly, increase the odds of a successful project!)
This weekend I'm working on an upcoming location scout the three of us are taking. More info to come!