Approach a nerdy guy directly.
Some nerdy guys may be unaccustomed to having women flirt with them, so it may take a direct comment to get the message across. Tell him you think he is cute. Be sincere. Nerdy guys are sometimes the target of unwarranted negative jokes in social settings, so the guy you approach may be wary.
Express interest in the things that interest the nerdy guy.
These may be subjects you aren't typically interested in but may find interesting to learn about. Open the door for his input. Show your interest sincerely and drop little flirtatious hints while you learn. Sitting close to him while he talks about his interests is one way. Subtle contact, such as a brush of your hand against his or your arm touching his while he speaks, may work.
Ask for his phone number and call him out of the blue.
He may be too shy to approach you. Take the lead and follow up on your initial approach to show you are serious about your interest in him. If you want to take it further, choose a date activity that fits his personality and ask him out.
- Avoid pretending to be nerdy yourself. Though this may work initially, you will eventually be found out and you'll risk making the guy you're interested in feel that you've played with him.