How can I get the most out of conferences? I recently attended a very large conference in my field (SfN, ~30,000 attendees), and after I got back I was thinking about what I had gained from the trip, and I realized not that much. I listened to a few different talks, and I saw a whole bunch of relevant posters, but on reflection I don't think anything I did progressed my knowledge/career that much. What should I do in the future to ensure that I make the most out of conferences?
Read this and this.

My professor put forth 3 simple rules for networking:


Talk to the guy beside you
Talk to top 3 (sort by relevance or whatever you prefer) presenters
Mail them 5 days after the conference with some follow up content (questions/comments/invites for talks etc.)


Just to make this post "dead-link" proof, I present a gist of the content in the above links.


Start Early. You should begin preparing before the conference starts. Start reading on who will be there, emailing people you want to meet, and determining which events you will attend. You may want to contact the speakers whose talks you will be attending before the conference; try to set up a meeting, or if they are too busy, at least meet them and give them your business card.
Bring Business Cards. Make sure they're up-to-date and details your preferred mode of communication.
Research people and get involved in their networks. If a certain professor is giving a talk; read his previous research papers, frame interesting questions and get an excuse to meet him. If you do meet him, exploit the opportunity to interact with his peers and try to enter their network. Sometimes, this is the only way of getting to network with someone. I know of professors who refuse to take students for PhD or internships or Postdocs without a recommendation from someone in his network. A good impression might just get you that recommendation.
Note people with similar interests to yours. These people will be attending all the same presentations as you, talking to the same people, discussing similar topics. They are the potential spots for networking.
Prepare the elevator speech. A common question will be "So, what is your research about?" Make sure you have an answer for every audience. For e.g. If you are in Computational Science, the answer may vary depending on who you are talking with. Plus, make it interesting and digestible. 
Organize an event of your own. This is especially useful is forming "lower" networks i.e. networks of people who lag in terms of age or experience such as graduate students. If not more, they could notify you of openings or interesting papers or whatever. They could be useful. (Plus it helps us :P )
Read "Never Eat Alone".
Follow Up. Prepare for this even before you leave for the conference. Have different modes of follow up ready. Will you have anything to say that is worth writing an email for? If not, think of something which will. If nothing works, make sure you click a photo of yourself with him and send it to him a few days after the conference.