As a writer, this happens all the time. The solution? Kick yourself in the booty and make yourself do it. :P Not necessarily the best solution, but it's the only one that works for me when I'm in a rut. I actually had to do it to myself with sewing last night--my OBW quilt has been waiting around for me to finish piecing the blocks, and I've just been a lazy pants. Well, today I'm going to finish them if it kills me!