I have also found having a song stuck in your head (that fits your natural tempo), is great for both endevors too (golf and pool).
I think the lack of thinking helps in both of my examples. I'm not worrying about coming up short for shape, or getting hooked behind a ball, etc. etc. etc. I hate when those thoughts pop into my head, and those negative things do all the time. Don't shoot this too hard, or what if the breakout doesn't come out well, and such. When I'm not thinking about that, it seems the negative stuff doesn't happen nearly as often. Best way to answer the OPs question is....when my head doesn't get in my way!!