Don't leave the coffee shop until you've had at least three positive social encouters. Practice. Stretch. Get comfortable being a little bit uncomfortable, and see what happens. One of my most significant romantic relationships started just this way. I saw him sitting at a nearby table, and our eyes kept finding each other.
Looking for some way to strike up a conversation, I noticed a book on his table that I'd heard about but hadn't yet read. Next time our eyes locked, I smiled and asked, "Hey, I noticed the book you're reading and it's on my list ... how is it?" He and I had a really gorgeous two-year relationship. If you're the "more feminine" woman who really wants the guy to make the first move, you'll want to practice signaling men (with your smile and your eye contact) to let him know you're open to having a conversation.
More from YourTango: How To Become A Date Whisperer
Have a blast. Have fun playing with your coffee shop flirting skills. Report back to let me know what's working for you.