What qualifications do I have to have to be a freelance writer?

I already have a blog and since I can't get a job for the summer, I can take a whack at some freelance writing jobs since I have nothing else that brings in money. What other qualifications are people who hire freelance writers look for? I am currently in my 4th year in college as a psychology major. If freelance writing is not gonna work, then what should I do for money this summer?