One thing that works for me. I keep a legal pad for each project I'm working on. I write a to do list in pencil on a sheet. When a task is complete I cross it out with red pencil.

So I say to myself just pick something and do it. The reward is the gratification of crossing it out. If a sheet gets filled up, I transcribe the remaining items to a new page, which engages visual, verbal and kinesthetic learning modes and refreshes my perspective on where I'm at with the project.

There is most always a space to the right of my mouse for the current pad. The system breaks down when that space gets cluttered for whatever reason. But when it's there I jot down tasks that come up while I'm coding. I keep the pads organized in a flat file that is just big enough to hold papers.

It works for me. Also getting enough sleep, exercise and eating properly helps.