One thing I've found helpful... and I don't know if it will help you because your problems could certainly be different... is to try to keep on to a single main point or two, and a limited number of sub-points. On every post I've made in the past few days, there's a lot more to be said (and a lot of the posts started out as one big long post on what I felt were related topics). Restricting the subject matter helps keep the whole post coherent and also helps you reach something that feels like a stopping point.