Credit card account closed and can't open it back up?

I signed up for this credit card during my freshmen year in college. At the time I didn't know too much about credit. Basically, I made some unwise choices which ended with my account being closed. I'm 22 now and really want to build my credit up. I send in a request to reopen my account but it was decline. I could easily pay the card off but I wanted to keep it, so lenders could see that I was actually using it. Where do I go from here? And also tips on how to build your credit up will also be helpful.