Staying out of debt again?

I was very high in credit card debt for being 20 due to an ex-boyfriend. But I cleaned it up and now I can start rebuilding my credit. I applied for a credit card cuz face it we need one in todays world to do anything. But if I get it fine, but if not then fine also I'll deal. BUT I am worried that I may start going crazy with it and get myself into debt again. What can I do so I don't?