It's about what humans want. Humans act the same, for the most part, accounting for cultural differences. (Fashion is an example of a cultural difference, In Turkey, for example, men often place as much importance on being stylish as American women do.)

So, think culture development. Talk To Customers. (And don't try to flirt. Look at their faces. Write notes.) Talk to them both individually and in groups.

Have a partner actually in the demographic.

This is common advice, but I find it frustratingly vague. Talk to people? I talk to people all the time. Heck, I talk to women all the time — half my friends are women, I currently live with two female housemates and used to live with a third, and my mother is a middle-aged office manager. After years of talking to them, I can only conclude that I've missed the boat on making Facebook, Etsy, The Sims and Model Mayhem.

I imagine a lot of people are in the same boat. It's hard to talk to people in a way that reveals product opportunities. That's why they make things for the only people who will actually tell them what they want — themselves.

You may find this a helpful starting point:

http://www.dlt.ri.gov/lmi/census/wf/female.htm

Shoes.