Nathan Bransford wrote an amazing article on his blog this week, about how one can tell whether or not one has talent when it comes to writing.
No, he does NOT give you a checklist, unfortunately.
He sparked a very intelligent discussion about whether or not talent is important to one's potential career as a writer. I personally believe that it doesn't mean a single thing whether or not a particular author has more "talent" than another.
Skill is much more important, as well as an ability to play to your own strengths.
True, real, honest genius is very rare. We may hear about two or three brilliant "talents", but for every single one of those, there are hundreds of thousands (if not millions) of people that swing between total failure and moderate success. If you were a genius, you would probably know.
In the absence of genius, skill can do almost all of the legwork for you. If you learn how to craft a sentence, a plot, a setting, and characters well, if you can learn how to work dialogue and description, you can really do quite a lot for yourself in the writing world. Spend time working your craft, learning how to do what it is you need to do to make your story work better... take classes, join critique groups, and find an editor if you can.
Also, using your strengths to your advantage will get you just as far. One of my writer friends has difficulty in writing a linear story. However, his world-building is absolutely amazing, so he's learned how to craft his stories to unfold as the world becomes more and more familiar to the reader. My weakness happens to be world-building, so I transferred myself out of high fantasy and moved onto urban fantasy, where I can use the world in which I live to make my story happen.
If you can focus on those two things, you can likely make your manuscripts a lot better. Don't worry about your talent... talent is a very subjective term, anyway, and it's mostly for history to nail down upon you instead of for you to take on yourself. Skill and strengths. Let them be your sword and shield.