I didn't learn any lessons from my first venture into live-action filmmaking was the thing about Being Prepared. Because the Tastes Like Tuna shoot was so problem-free and enjoyable, I completely forgot how much preparation had gone into it. And when I next tried to make a film with actors and lights and real movement I assumed that as I was some kind of natural born cinematic genius, it would be similarly piss-easy.
This is how you don't do it:
When somebody shows interest in your script and says that if you fund it, they'll act as producer - double check that they're not just joking around. What you don't want is somebody who, when you phone them at 2 a.m after the first day's shoot with an urgent transport problem, says "I'm not the producer of this film."
Don't write a part for an actor - especially not the lead role - if you've never seen him act. Just thinking he's very photogenic and has a certain charisma is not enough. YOU HAVE TO SEE HIM ACT.
Make a storyboard. "But I can see it in my head, and I'm totally going to remember which angles we need to cover and the shots we've done. And no, we don't need anybody attending to continuity." You are wrong.
Learn something about lighting. Have a rough idea of how many lights, stands, flags and other bits of lighting kit you're going to actually need; don't tell the director of photography to "just get what you think will be necessary" unless you REALLY REALLY trust that they know what they're doing. Because they don't need all that stuff, no matter how much they might want it.
Appoint a director of photography that you REALLY REALLY trust. It doesn't matter how pretty she is.
Bright orange is not a good colour for the walls of a bedroom.
If you arrive at the first location at six in the morning to find a human turd on the doorstep, you might want to listen to the little voice in your head whispering about omens.
Really do make a storyboard.
If your lead actor has to do a simulated sex scene with your lead actress that requires his head to be in the vicinity of her thighs, it's a good idea to remind the actor that he's not actually supposed to go down on her for real. You might think it would be obvious, what with him being surrounded by lights and a dozen people, but apparently you sometimes have to point out that IT'S NOT THAT KIND OF FILM.
Trying to record sound at the same time as recording pictures is humanly impossible. Write a silent movie if you can.
If, after two days of shooting, it is obvious that the film you're trying to make is going to turn out to be a huge pile of shit, by all means stop trying to make it. If somebody in the crew tells you you MUST continue because everybody has worked so hard so far, let that person know that he can fuck right off. He's not the one who's going to experience screaming night terrors for the next two months.
Try not to cry in front of people.
And seriously: make a storyboard.