I try to write a little every day. Writing every day forces me to keep the day-to-day goals small and manageable.
The main reason I try to write everyday is to force myself to keep my goals low. Too big goals and I will end up putting writing of until I have more time. If I wait too long I end up putting to much pressure on the writing session which makes it almost impossible to sit down.
For the same reason I try too keep my current project easy to get into and just as easy to put down. It might sound counter intuitive, but the less I *must* do something, the more I feel like doing it, and the more I enjoy it.
The other reason that I try to write every day is that no matter how little I do, writing every day accumulates a lot of written words over a year.
I will admit to taking some days of now and then. It is easy to get lost in the doing. Sometimes I need a break to evaluate if I am doing the right thing, and if I am doing it for the right reason.