Twitter helps me around this issue with a strict character limit. Tumblr creates an environment where visual expression is emphasized and text boxes are very small. Constraints often breed creativity because they force you to improvise — to think differently. But self-restraint is just as important. And harnessed correctly, it can yield far greater results.
I often think of Twitter and Tumblr this same way, however, I rarely edit my own posts with any form of brevity in mind. Great short read from MG Siegler.