You're really lucky, I had to save a few months to start up my operation which only started with about $300. The first step is to create a business plan, as others have said. Just a few tips from me:
- think sustainability: you have 50K now, develop a business model where you can get a steady stream of income, rather than fall for 'get rich quick' schemes
- be a visionary: study your environment and the opportunities present. I have a friend who did that, in my home country they are going to pass a law regulating water treatment in people's homes by 2014. I have a friend who opened a business in that area and he's doing very well, and will continue to do well for the next 4-5 years at least
- do something you love: starting a business is tough. very tough. you've got to work without counting the hours, and in order to do that,; you've got to do something you love. Or else it'll drive you nuts.
Best of luck, and don't get scammed!