I... type... stuff? xD
But yes, for me at least, my latest post is a bit on the shorter side by my standards. Although, I suppose you could call it a medium-sized post too, given that oen paragraph was ridiculously long compared to some of the others.
As for how to write longer posts, you should only do so if you have things for your character to do, say and/or think. Posts filled with no substance or meaning are rather uninteresting to read.
But if you want a good example, just look at Lugu's latest post - I really liked it.

He had his character mentally comment on each of the other characters, remenisce about his own creator as well as consider and contemplate the meaning and actions of Rodias. It was a great way to bring the character to life and give us an insight into how Graft thinks and feels about everyone around him, as well as how he responds and views the current situation.

So, yeah... Do that, if you want longer posts, I guess? :P