Very often, it’s the start that is the most difficult part! Even when you don’t feel like working on something, pushing yourself to get started can often shake off the last vestiges of resistance and put you on the right track again.
I like to play a little trick on myself: when I really don’t feel like working on something, I’ll tell myself that I have to put in at least 15 minutes of time on it. I promise myself that if, after 15 minutes have passed I still don’t want to keep working on it, I can stop. This almost always works for me. Once I get involved in what I’m doing I have no trouble keeping up the momentum.
Whatever you have to do to “trick” yourself into getting started, do it. Once you’re rolling along, you probably won’t want to stop.