For me, it's having an agenda with one item on it prepared the night before. The last hour before bed I review the code, screens, and notes from that day and decide the most important thing to work on the next day. Then I lay it out in detail including a red marker on my code. When I get to my computer the next day, I'm ready to go. Sounds simple, and it is. It's also very effective.

Coffee. It's like turning on a light switch.

Completing a small but significant task first thing in the morning often sets the tone right for the day and imbues a feeling of satisfaction.