The best piece of advice I could give, is to plan and to read. Planning key points of your character's story in advance means that you know where you're headed. It's okay to take diversions on the way there, but it's important your character's storylines aren't just thrown together or it'll seem really disjointed. Be confident in your ability, and as Finn says, read the stories of the top guys. Go back and read old work too. A lot of today's RPing is focused on trash talk, but my personal favourite RPs often focus on character development, or a combination of both. Sebastian Duke (or Thaddeus) is a good example of a character who clearly has his development and plot twists planned out, and it shows.