Number one tip, and one that especially applies to "nerds": Girls are people. Stop seeing them as "girls", and accept that they're pretty much the same as you; same insecurities; same faults; same fears.
We're all looking for the same thing, so don't be afraid to show interest in a girl. It doesn't make you a "perv" if you smile at a girl you like, it doesn't make you weird. You're allowed to send signals, you're allowed to flirt, just don't expect it to always work. Be prepared to get turned down. Everyone has to go through that, and you're no exception. It's not because you're "different" or "broken" or "weird", it's just that you're probably not compatible with that person, and she doesn't want to waste her time or yours.
My 5¢.