Have the characteristics she finds attractive, or pretend to. That's what interest level means.
Usually she either is interested or she isn't, and if she isn't interested now she probably won't be further down the line. Usually the only time an IL suddenly increases is if you don't see each other for a while and you've changed significantly in the interim, but even that's not common.
You could try eliciting her values and then moulding yourself into the kind of guy she likes, but (1) that compromises your identity and (2) she'll probably see through it and be less attracted to you.
[edit] Of course, I'm assuming her IL is set already, i.e. she's interacted with you enough to know (or think she knows) she's not into you. If you haven't interacted much, then it's entirely possible that she's on the fence, in which case just show her your personality or a pretend one and see how she reacts. Just ask her out and see what happens.
