I either assign them a time, like 20 minutes a day or work on them on Sunday. A lot of my UFOs get finished a few blocks at a time. That blue and yellow string quilt gets a few blocks added everytime I pull it out. When there are enough blocks, it'll get a string or two for every block. Someday it will hit the 20 minute a day category and be finished.
Course I enjoy the process as much as the finished project.