How can I make sure I qualify for the American Opportunity Credit? I qualify but have never been able to receive the credit.

Try the IRS' Interactive Tax Assistant for education credit, and see what it tells you. This should tell you if you qualify and if not, why not.

If you are eligible, you have answered  something wrong, in the interview. But, a lot of people are just not eligible. See https://www.irs.gov/Individuals/AOTC

You cannot claim a credit if you are, or can be, claimed as a dependent by someone else

A full time unmarried student, under age 24, regardless of whether he can be claimed as a dependent, or not,  is only eligible for the refundable portion of the American Opportunity (Tax)  Credit (AOTC) if he supports himself by working. You cannot be supporting yourself on parental support, 529 plans or student loans & grants. You usually must have actually paid tuition, not had it paid by scholarships & grants.  It is usually best if the parent claims that credit. 

List the factors that make you think you qualify for the AOTC.