4- Read her body language
There are many different signs and subtleties depending on the situation. Just remember that, like you, if she fidgets or taps things, she's nervous in an uncomfortable — i.e. potentially uninterested — way. If she licks her lips (consciously or not), runs her hands through or shakes out her hair, or, one of my favorites, plays with her earlobe, she's sending you buying signals.
What about smiling? It's good, right?
Well, only the right kind of smile. If she shows her teeth and laughs openly, you're on the right track. If, on the other hand, she doesn't show teeth, or she looks away when she smiles, she's probably just being polite, possibly because you're boring her.