1) Target one individual or small group beforehand and interact with them. This could be a YC partner, a YC founder, or a future cofounder. Don't follow them around like a dog, but make an effort to schedule a follow up meeting or phone call with this individual, get on their radar, and strike up a meaningful conversation.
2) Don't have a "plan" -- just go to meet cool people. You never know what will happen. Have a 1-2 sentence blurb prepared about who you are, and what you do (or what you're building), and don't be shy. Everyone's as awkward as you are at these things :)
I've gotten jobs from both, and richer networks from #2.
With just the right info. One to lend.