I am generally more productive when I first get in, so I like to draw up a to-do list for the day. I organize my day around the "big rocks" metaphor, working around the important or urgent projects, and fill in the holes with the less pressing tasks. I find that marking those big tasks off my list gives me not only a sense of accomplishment, but a good opportunity to stand up, walk around, and say hello to a coworker before I tackle the next one.
