I have found that I have some very productive times when I feel like I can get a bit of work done on my paintings almost every day, but there are other times, when it just doesn't happen. However, those times I usually try to be productive in other ways. I work on my websites, write this blog, or just think!
Thinking is an underrated part of the creative process. I like to always know what I am doing next, to keep one step ahead of myself. Most of the time it works. Sometimes you just run out of steam on all fronts. But that's ok, too. Just have faith that the juices will flow again soon. I used to get a bit depressed during those times, but I've been through it enough now to know it always comes back.