Of course you can do short! I signed up for seasonal_spuffy, partly because I had an idea for a short fic (that ties in with another fic, but that works as a standalone), and now that it's written down it's a neat 2500 words. It needs editing of course, but it won't get much longer.

So you could try something like that maybe? A sidestory to some of your existing fic, or a scene you had an idea for but that didn't/wouldn't fit f.ex. And drabble series are a v. good exercise. :)