1. Put your own work first. Write the monograph and half of the second one before you even think about doing the edited collection.
2. Prioritize the large project over small ones, and small ones over insignificant ones. So be working on the major project at all times, not peripheral ones. Articles take precedence over book reviews. Articles that put forward your main research agenda take precedence over those that don't.
3. Don't wait until you have large blocks of time to resume work on your major project. Since you only need 1-3 hours a day for writing, and it is actually harder to find those hours when you don't have other structure in your life, you are likely to do better if you already have the rhythm of work established before that summer break or sabbatical.