What do I say?

How do you start a conversation with people? I'm fairly sure all the conversations I've been in with people I don't know were the result of introductions or they talked to me.

Worse is the fear of talking to people who I know (I've met and talked to them a couple of times), but I can't seem to start a conversation outside of a dark, smoke-and-alcohol filled room. It may just be I'm in a hurry for lectures. But I avoid them, I don't know what to say. It does feel wrong to stride past them on the way to campus, but I can't face them somehow.

I shouldn't post this late, sleepy time awaits. [snore]