I've noticed that for me it depends greatly on what my character is doing at the moment, and who's he interacting with, if I write more or less.
When I'm interacting with my RP partners character, like a conversation or something along those lines, then my posts are usually rather short. There's only so much additional info you can give to the actual sentence your character says. I mean you can't describe how he stands with every sentence, or what he sees, etc.
So sometimes its really just one line, but usually it makes sense in those circumstances.
Then when my character is doing things on his/her own, or interacting with NPCs, then my posts are generally alot longer. Thats mainly because you can describe more actions now. I do this, and then I do something else, and after that I do maybe this. Or in a conversation with NPCs, I can have both sides say something etc etc.
Also when my character has some control over another players character. For example she's tied up, so my char can do things to her that in normal situations would be godmoding. That generally results in longer posts too.
However I try not to overdo it and stop at one point, especially in that last case, to give the other writer a chance to do something as well.
Well thats how I do it, there's not really a wrong or right style of roleplay and others do it differently. But as consortium said, just writing long for the sake of long is more damaging to the whole thing than helping
