Competence, plain and simple. I do not expect long, drawn out posts that go on for days (I actually detest that if done regularly) but I do expect a modicum of creativity and an understanding of the English language so we don't have to struggle reading your writing. Or at least an understanding of Google to check that your sentences make sense. Make the posts as long or short as you want within reason and use whatever pacing you feel like. Just write like each of your posts helps toward a common goal to advance the main character in an interesting and half-meaningful way. Just that behavior alone is great. 

Hope that was a helpful answer ^^