I'm a competitive casual myself, but I think I still might be able to offer you some helpful advice. What you want to do first is join a Smashcord of your mains and/or secondaries if you haven't already. This way, you'll be able to build up your experience with your characters, allowing you to soar to greater heights. You should practice daily, and have people critique your gameplay so that you can see where you went wrong and how to improve it. Learn matchups and stage strategies, too. Also, be sure to register in as much online tourneys as possible so that you can get an idea what it feels like to play competitively against other players. Or, if you just absolutely despise online tourneys, then try to go to as much locals as you can. Hope this helps!