The real difficulty is in recognizing that you are stuck. You might be working on 10 different things. You may be making or ogress on 9/10 things. However the one thing that gets stuck may be holding you back on milestones. I've noticed in the past that I would put more effort to get the other 9 things going faster than put an effort to recognize that I'm stuck on a task and that's really important to achieve the milestone. I would be avoiding the task without even being aware of it. A personal project plan helps me notice the lack of progess on a task. I've been reading "Getting things done" by David Allen. Listing out things you need to get done and inventorying them periodically helps me to a certain extent.