In order to be a good working actor I think you need to think of yourself as an athlete. Work out, eat well, build up your body and immune system and generally treat yourself as an athlete.
I was standing in on a indie film and the lead male character was a very fit, high powered, business type. As part of a montage there was a shot of him running full speed on a treadmill. In order to get this the lead male actor had to run at an incredibly fast speed on and off for about 40 minutes. In between shots and lighting changes his stand-in also had to run at top speed. They both had to be in really good shape, or be willing to push through and hope to not have anything major to do the next day. And I thought: god….I have to start working out more.
I talked to CP (my husband / a camera operator) about this and he said that the best camera ops / DP’s (director of photography, position above camera op) are people who treat themselves as athletes. They eat really healthy meals, when they go to crafty they hit up the protein/veg. They drink plenty of water, they work out and they take precautions to prevent injury / sickness.
This is a big part of the reason we rejoined the gym. 🙂