To the Actor #16: My Set is Not Your Homework.
An actor must always be learning, always striving to better themselves, always working at their craft, fine-tuning, trying new things, divesting themselves of old things. This is the nature of the actor, or at the very least should be.
However, when you step onto a set, playtime is over, lesson time is over. At the end of the day you should definitely look back and reflect on what worked, what you might take from the day, what you can do better, but that's at the end of the day. What you can't do is spend the day on set 'practicing.'
This is tantamount to a surgeon stepping up to take out your kidney and saying to the nurse, "I read about this new way to tie-off sutures yesterday in my most recent journal. I'm going to try it out on this patient."
In medicine that's a lawsuit waiting to happen. In acting, it means your going to look like you've got your head up someone's indelicate orifice.
You weren’t hired to explore your craft. You do that on your own time. You were hired you to act. So act. Forget about what you did in acting class two weeks ago. Forget about the new sense memory bit you read in Chekhov's recent acting book. If you don't 'know' it by the time you're on set, you're doing a disservice to your craft and a disservice to the production at hand.
Have you ever stopped to think how you can do the #1 thing an actor must do - to be present - when you're trying to figure out if you've got enough breath behind the word 'titillate' or if that mannerism that came out during rehearsals is big enough (or small enough?) You can't!
Throw it all out, be present in the room, and friggin' act. It must be natural and honest first and foremost, everything else must be built on that foundation. If it isn't it's unpleasant to watch.
This, in itself, is the difference between an actor who is and someone who wishes to be.