If I find myself staring at a post unsure what to write, I put it off. Give it a few hours or a day, maybe two. Focus on other things, probably gaming for me. (though lately it's been lugging stuff from old apartment to new apartment) Or sometimes I play around on Tumblr. Eventually I go back, re-read a few posts to refresh the events in my head and usually by that point I can get a good post going.

If not I talk to my RP partner about what I can do next, usually that at least gets the juices flowing and communicates to my partner I'm hitting a small snag creativity wise. Two birds with one stone. :P