Seriously. I haven't seen anyone really talk about this before, and I don't know why. A good smile is an invaluable asset.

Think back to the last time a girl smiled at you and how you felt about it. If she was anyone you were even decently interested in, it probably left a good feeling in you. You can do the same to girls. Woah.

"But sharkacolypse, I look like a creeper when I smile!"

Then practice in front of a mirror. Really. Go do it until a non creepy smile is built into your muscle memory.

If you can make eye contact with a girl, smile at her, and have her smile back, that's generally a sign that if you approach you will not be immediately turned away. This works great at bars, parties, or anywhere else where there could be distance or obstacles between you and her.