Ask HN: How do you allocate time to your (pet) projects and interests?

How do you decide how much time to spend on a given project, and wether to follow it at all? I find that if I were to pursue all the little ideas, projects, and interests I come across, I would probably be unable to effectively do any of them. What I end up doing is discarding most of them, or at best jotting them down in a notebook, but it is very unlikely that they will be pulled back out from there. The ones that I do pursue, I do try to do properly, but the selection is rather random, made on a whim. Surely many people here on HN have the same problem. Have you come up with any more creative approaches to this? It seems there must be a more proportional way than my all or nothing method.