If you're having issues try reading through these pages and pick a few people's suggestions that you think might help you.  Now make an Interest Check (if you really want to GM a new RP) or type up a Character Sheet for an RP you want to join...while keeping these issues in mind.  Consider it an exercise.  If you focus on improving your writing on those basis...es you will likely see some improvement.

You might consider just writing a short story or two instead too.  Short Stories make good Interest Checks.  You could also always start another little Short Story Contest, or do like a Short Story Starter Thread where you post a Short Story, someone posts some feedback and a starter and then you post another Short Story based on that starter.  Or you could do the same thing and trade off who posts the starters and who posts the stories.  Good way to meet people and start getting known better.