This was a very close subject during the recent challenge. I would find other things to distract me (Skyrim) and wander away from doing what I was supposed to do. What I found that helped me is that I would force myself to sit down, read all my forums once, and then open the map. Usually if I did something, even if it didn't work out, I *did something*. From there it became easier to cascade into a lot of doing something. Some of my most productive days were ones that I had to literally force myself to focus. So I suppose I am in the "matter of sheer will power" group. Wanting to get something done more than whatever distraction you've got going also helps.

I've never had to work for somebody else creatively, but considering how I am good at meeting work deadlines, I suspect that would be a help too.