Say you go into Starbucks and there's a long line of customers waiting to order a drink. Approach the end of the line and go "Whoah, long line!". Chances are, you'll get someone's attention. People will turn around and look at you. When they do, make eye contact and say "We're gonna be here a while!" or something like that. You're immediately building rapport by referencing a shared context, as well as broadcasting your own confidence and willingness to socialize. It works great.

A more difficult scenario, but still quite doable, is a bookstore. Find someone reading a particular book or type of book, or looking through a certain section, and engage them on it. "Hey, good book!" They're looking through the psychology section? Say "Psshh, Descartes. What did HE know?" This sort of thing will elicit a smile from almost anyone. The important thing is to not LOOK awkward, even though you may feel awkward.

Yes, this approach is cheesy. And some people may find you annoying. But those are people who are likely annoyed with life in general. Overall, you can generate a lot of positive results this way. If you want to generate maximum socialization, be THAT guy.