If I see something I like I will take a mental note of it, try to find it on the internet, and play around with finding pieces to style it with. (blog.10pm.nyc)
If she's vegetarian, make a mental note of it. (datingadvice.com)
If you can't do this, then pay attention to their shoes and make a mental note of them, or even create a sketch. (edutopia.org)