Working on coding and designing levels can be a lot of fun. However, there are times when you really have to drag yourself to keep on task. Admittingly, I'm pretty bad for not dragging myself through. The worse culprtis are when I'm just not in the mood, or I have to tackle one of those 'not-so-fun' tasks.
Not being in the creative or productive mood is often remedied by doing something a little smaller, then using the satisfaction of completing that to continue onto bigger tasks. If there are no small tasks that I can think of, I often just start reading lolcats instead.
It's the 'not-so-fun' things that are killer. Sometimes you need to redo a big portion of code or building that you've already done. Redoing stuff just for a slight change in the end doesn't provide much satisfaction. Still, entirely necessary.
Anyhow, I've found a better solution for both of these. Pick up an agenda book and schedule some time. It does an amazing job. In fact, it's the reason I just got around to writing this!
Let us hope that I actually continue to use the book.