I've found it extraodinarily helpful to divide my day into phases, each responsible for a different domain in my life. For instance, I have the tags phase-work, phase-work-tedious, phase-home, and phase-personal.

Each morning, I tag the items I realistically feel I can accomplish in the day with the appropriate phase. I'm careful to divide my work evenly among the phases, as this represents an appropriate balance in my life. Then I will work through one phase at a time, completing everything in that phase before moving on to the next.

I use the smart list "tag:phase-foo AND (due:none OR dueBefore:tomorrow)" to see everything I need to do for phase foo.