I'll give you two possibilities to get started:
1. For example, develop some level of expertise in the architectural history of where you live. Architecture is aesthetic, yet manly. Not that many girls know much about architecture relative to their other aesthetic interests, but they are naggingly aware that they should know more. (Obviously, if you live in Chicago, you will have more to talk about than if you live in Palmdale, so your mileage may vary.) For example, the recent indie romantic-drama hit, 500 Days of Summer, uses architectural fandom, with LA's rather spotty downtown carefully framed to look like downtown Chicago, as the basis for a rather nerdy young man's appeal to Zoey Deschanel.
An interest in architecture also provides a high-minded excuse to talk about what every 20 or 30 something is actually fascinated by: real estate. What neighborhoods will go up in value, which ones down? Architecture appreciation provides an excuse to stroll around gentrifying but still slightly edgy neighborhoods on cheap dates.
2. Read Pride and Prejudice by Jane Austen (or at least watch one of the 3 movie/TV adaptions of the last two decades). It's really witty, it's increasingly influential (it's the touchstone for popularizations of evolutionary psychology, among much else), and it will teach you a lot about the feminine mind. Plus, girls like it!
Now, what's the worst that could happen? These two suggestions might totally fail to help you with the ladies, but you will still have learned something of the architecture of your town and you will have read one of the great books in the English language.
That about exhausts my list of suggestions. What are yours?
