Finding CG's is a learned process
I had always wondered why guys even ask on how to find them, because to me they are so obvious. However, last year, I went to Vegas with a bunch of people from work. We were walking thru one of the casinos, and I exclaimed "holy shit!" because there were lots more CG's than I had seen in quite awhile, and hot WCG's at that. The guys from work were puzzled and said "yeah, right" and "in your dreams! In an attempt to prove it to them, I stopped the group, said "watch this" and chatted one up. They still wouldn't believe me. Told me I had an inflated ego and the girl was just tolerating my come on.
It was then that I realized that knowing how to clearly spot them is not obvious to the average Joe. I can take a brisk walk thru and find them all. As the previous poster said, to make sure, make eye contact and smile. If you get a smile back, chat her up.