When you hit 30

Don't go into ranked immediately. I know, you've waited 30 levels and countless hours so you can play ranked, and you want to jump on it because you're so excited to play it. Don't. You'll regret it when you have to drag yourself out of Bronze and you'll regret it when you run headlong into people who are ten times better than the people you just finished playing against pre-30. So instead, play some Draft and Normals and get better before taking the plunge. Your patience will be rewarded.