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?
From my own experience I get the most out of conferences which are not organized as conference expos. There's a big difference between conferences created for income (yes, even in academia) and those created to promote new discoveries and knowledge.
Of the latter type I find the presenters are generally excited by their opportunity to meet others in their field. It's more of a grassroots type of experience and you find that you naturally start to share in the discussions. No networking is needed.
What should I do in the future to ensure that I make the most out of conferences?
Choose a conference that's in your field. Prepare a paper or two of your own on a subject that really interests you. Discuss it with colleagues. Get it published. Present it at a conference. The critical thought you put into this process will help you to pick conferences more suited to you and stimulate your interaction with others.