Two good posts about writing: one at Daily Practice and the other at Just Tenured. The key for both is to keep writing, whether that involves starting the day with writing that can be "just practice" or keeping a timer going to keep you honest about your work.
I like both of these ideas (and the other ideas in the posts as well). When I've tried the timer method before, I tend to cheat: "Must check Expedia for air fares now," says my brain, or "You surely can't mean to go on with this piece of writing until you look up the serial publication data for this novel." My fingers comprehend this instantly and spring into action, and before you can say "Firefox" I've left the writing behind. My new plan is to note these traitorous brain flares on a Post-It and look them up only after the time is up.
The daily practice should be good, too. What happens too often with writing is that you start in the morning and end up borne away on a huge wave of unavoidable distractions--meetings, classes, and so on--until you wash up on the beach miles from wherever your ideas were earlier in the day. Daily practice might help to keep that early morning focus.