start by simply explaining to yourself what you want the characters to be like, where your story takes place, what the conflict is, etc.
personally, i hate seeing bricks of text in the writing arena.
go back and reread everything as you write. try to keep it short (concise) and sweet. decent grammar is also appreciated.
my favorite piece of advice:
when you reread everything, do it in Morgan Freeman's voice. if your story inst intriguing and flowing then you goof'd.