I think my biggest fears are 1. I say something early on that makes me seem like a fool or needy. 2. I try to push the envelope too quickly therefore freaking her out. 3. Trying to rush her and/or thinking she isnt really interested or something since she wasnt available to talk in other words always thinking somethings wrong.
As being needy yes, that can chase women away even when you didn't mean to. Pushing the envelope will definitely freak her out and you know better than to do.
Other than that if she's into you, unless you mess up real bad, ya can't really do that much wrong.