Keep track of my accomplishments. I usually set a goal I can measure with a number.
Take short breaks: the keyword is short and not break. I don't believe in 9 to 5 hours, that's for wimps :-p.
Keep good snacks around: I try to drink something tasty while working.
Minimize distractions: easy say, hard do.
Finish ASAP: I try to complete tasks (broken into small) in energetic spurs.