The only constant I can find is hard work.
On 'There Will Be Blood,' I was cast at the last minute. I had 3 and a half to 4 days to get ready for the first day. I just went for it, threw myself in there and gave it everything I had. That was just guts and instinct, not a lot of preparation.
In life, you have to keep certain parts of yourself in check because you want to be a decent human being. But one of the guilty pleasures of acting is that sometimes you get to let a little something out that you don't in life because it's not right.