Make sure you use proper spelling. Always think about what you next post will be, and think of ways to flesh them out. For example:
" She smelled deer. She got ready to hunt." <- this is an example of a non-literate post. It still makes a point, but is lacking description.
" She came to attention as the musky scent of deer filled her nostrils, combining with the scent of the rain. Excitement at the prospect of a hunt filled her body; it took everything she had to stop from bolting after her prey. She turned to the group behind her, awaiting the signal." <- This post says the exact same thing as the previous one, but which one is better? This post give the reader more of a description of what your character is going though. This is an example of a roleplay post I would use in game.
A good guideline is think of what you want to accomplish, and add description of different senses in. What does your character smell? See? Feel? In my second example you could tell it is raining, that the deer smells musky, that she is excited to be hunting, and that she is not the one in charge, and in only three sentences. It takes practice, and I am by no means a master of it, but if you try hard, you will succeed.