One of the things I find helpful for me is to write a doable to do list out when I get to work. After each task I complete, I'll get up and take a short break and get up and walk around for a few minutes to try to get my blood moving a bit.

Also, I don't usually have strict deadlines for a lot of my work load. On my bad days I'll tackle all the stuff that I can practically do in my sleep, and then on my better days tackle all the stuff that needs more concentration and social interaction. I do this as much as possible. It's not always possible, but it helps me.