Sometimes it is very hard to meet people at conferences, networking events, etc. I've been doing this for quite some time as a consultant, so there are a lot of lessons that I have learned and even some that I still can't quite get over. That being said, it is always important to be mindful of a few things are very important.
Be courteous: No matter who it is you are talking to, treat them with respect and a little bit of class. There is worse than that feeling. The truth is, you never know at any point in your career that you might cross paths with that person and that first and lasting impression could make or break that meeting.
Listen & Pay Attention: Stop talking and listen! I can't tell you how many times I've done this or been victim of this. In the past I would totally just blabber away and not really pay attention to the person I am talking to or have someone do this to me. It is quite annoying and as with anything else, leaves a bad impression
It's o.k. to be nervous: Sometimes people tense up and get nervous at these events. This is completely fine and normal, there is absolutely no need to freak out. I remember my first conference, I was so nervous to talk to anyone because I didn't feel "good enough" to be there, that I basically just curled up in a ball with my laptop and worked. DO NOT, I repeat, DO NOT do this!!
Business cards: Recently at PubCon 2007 someone told me..."ohhh, I don't do the whole business card thing..." also at a couple of other events in the Bay Area recently I have run into countless situations where people were not prepared. The truth is, if you are at an event where you are trying to build on connections, business cards are crucial to staying in touch with people.
Follow Up: Always, Always, Always follow up with the people that you meet at an event. My best practice for this is doing a mass add of people to LinkedIn and send out an email the night of or day after an event. I would say within 24 hours is a good rule of thumb. To add to that, if you are at a conference, definitely continue to add and get in touch with the connections you make because they are fresh on the mind at that point. Also, if someone gets in touch with you, the same rule should apply, follow up with that person within 24 hours.
A lot of times the rules above can be tweaked and adjusted per industry and your needs. But, just be sure that you are applying them in whatever way you see fit.