The quick way would be to pick up "Visionmongers" by David duChemin. I can't recommend his books and ebooks enough - he's a great writer with his head on straight about what's important. In the book, he gives a lot of great advice for making the transition from hobbyist to pro. It's realistic and fun to read (he was a professional comedian for 15 years - ha ha).

The long answer would be to take business classes - sales, marketing, accounting, planning, stuff like that. This is the weakest area of my business. By the grace of God, we make money doing this, but it could be more profitable if I was better at business. ;)