One thing you might try considering is possibly making your posts shorter? I haven't read any of yours recently, but if you've noticed that you tend to focus on one topic at a time, work with that instead of trying to work against it.
Or, consider writing posts in segments, maybe with bullet points to help you out. Figure out what the overall theme of the post/story will be, then break it down and tackle it in sections? I don't do well when trying to set scene alongside character introspection, so I avoid doing both at the same time, and just combine them into the same post before putting it up.

As for tackling run on sentences and sentence fragments - might try restricting sentences and make sure you only have one agent (acting character), one recipient, and one action? This can be expanded up towards two, but if you go more than two - especially in the case of agents - things get messy. Hope this helps, even if just a little bit.