Or: Don't Do What I Did
The following is a list of tips derived from what I think has helped me enjoy computer science conferences more (and possibly learn more from them) as time has passed. I don't assume that they will be helpful to anybody else, but perhaps they're worth thinking about! I expect this list will be the most useful for grad students starting out, and other people who haven't gone to conferences before. If you are more experienced, you can always tell me why I'm wrong or whatever.
1. Pace yourself.
Skip talks. No, really. Going to every talk should not be your goal. Most people can't go to every talk and understand everything. (Don't even expect to understand everything in any one talk.)
Try to highlight talks you especially want to go to in the program in advance. You can do this during the first coffee break or during the first talk when you get there halfway through; it's okay :) Be open to adding or dropping talks (adding can be if someone tells you "hey, X's talk is going to be good" or if you happen to see the beginning and are drawn in; dropping can be if you feel tired, want to get some exercise, or get into a good conversation with somebody). I promise you that even if your school or employer is paying, nobody is going to exhaustively quiz you on the contents of every talk when you get home.
2. Pace around.
If it's possible -- not too rude and disruptive given the room layout, and physically possible for you -- try pacing around while you're listening to talks. At ICFP this year, the room had a big space in the back without chairs, which some people used for standing, lying down, doing yoga, and other such things. I don't know if this was intentional, but it worked well. Sitting in the same position all day is not good for most bodies. Don't be afraid to move, stretch, or even sit on the floor or lie down while listening to talks. If you're me (and possibly even if you're not me), this will help you listen better. Just because most people are sitting (too close together, on chairs that are probably uncomfortable) doesn't mean you have to.
Another advantage of standing is that it discourages you from opening your laptop, if that's a compulsion for you.
3. Take notes.
Not everybody focuses better while taking notes, but I certainly do; if my hand isn't moving, my mind checks out. But taking notes does more harm than good unless you do it effectively. it took me years to learn that note-taking isn't about writing down what the speaker says in complete sentences. If you hear something that makes you think, "That's interesting! I wonder...", write it down. If you hear something you want to read more about, write it down. Notes can be illegible to anyone else (so long as you can read them later!), in incomplete sentences, structured as bullet lists, etc. Nobody else gets to see your notes unless you let them.
Sometimes notes are write-only, and that's totally okay. You might never look at them again, but the act of writing will still have helped you remember what you learned.
4. If you don't understand, assume that it's not your fault.
This doesn't mean getting aggro at the speaker because they were unclear. It does mean not bearing all of the blame for every single talk you don't follow. It also means asking questions (sometimes) without thinking it will expose your horrible ignorance. Chances are, if you have a question in mind, ten other people do and won't want to say it. If you ask, you'll be helping all of them.
It's possible that it is your fault, but more often, somebody just didn't put in the time/didn't do practice talks/other things to improve talk quality. At least at the conferences I go to, papers are selected solely based on the quality of the ideas and writing, not the talk (since when the authors submit the paper, they haven't prepared the talk yet!) Someone can write a great paper with a great ideas, but still have no idea how to organize slides visually or structure a talk. The academic system affords very few incentives to learn how to do that, other than an individual's intrinsic motivation and/or peer pressure.
5. If you can't pay attention to the content, critique style -- INSIDE YOUR HEAD.
I mean, it's educational for you to think about what methods do and don't work for slides ("wow, that hot pink background with white text is hard to read..." "wow, I don't like Comic Sans and only SPJ gets a pass"), but just to be clear, nobody else (especially not the speaker) wants to hear your bikeshedding. That said, I find this is a way for me to actually get more out of the talk content, because if I'm noticing how I could have done the talk better from a purely visual POV, I'm not thinking about how much of a doof I am for not understanding the content.
6. If possible, stay physically nearby.
At least at the conferences I go to, the conference is usually at a hotel, and you can also stay at the hotel, though the hotel the conference is in is usually outrageously expensive (not an issue if your research grant or company gives you an unlimited budget, but for grad students, faculty at small schools, and unaffiliated people, that can be a problem). That means you can theoretically travel to an exciting, cosmpolitan city for a conference, and never leave the hotel except to go back and forth to the airport (if you're willing to eat hotel restaurant food). The drawback is that there are usually much cheaper options, but generally a significant distance from the conference. It's up to you to set your own budget priorities, but even though I wish they weren't so exorbitantly priced, there really are advantages to staying in the same hotel as the conference. This is true even in European cities where you can walk or take an easy light rail ride everywhere -- the time it takes will add up, and you're spending enough time attending, going to dinner, and staying out late shooting the breeze that every minute counts (and sleep is crucial to everything else working out).
Staying at the hotel also makes it easier to show up on time for the first talk in the morning, which saves you guilt about missing it (especially if the conference puts invited talks first, which is cruel and unusual punishment if you ask me -- signalling that a talk is expected to be especially good by scheduling it at a time when it's difficult for many of us to be awake). It also makes it a snap to go back to your room for a nap, break, or just some alone time when you need it.
7. Know your limits.
I don't mean alcohol so much as people and new information. It's okay to tell yourself that your brain is full and go take a break. (Taking notes makes this easier, since you know you'll be able to resume easily.) This is true whether you're an introvert, extrovert, or the (probably-majority of us) who don't fit neatly into one of those categories. The limits may vary wildly for different people, but almost everyone has them. When you hit your limit, you'll know.
8. Ask questions.
Many conferences have a few people who seem to dominate the Q&A sessions for almost every talk. Session chairs usually know this, and some will try to call on less familiar faces. But for that to work, people have to step up. So every question you ask -- as an outsider, newcomer, or whatever -- means that many more fresh perspectives that the whole conference gets to hear.
Often, not everybody gets to talk in a given Q&A session, but it's okay and encouraged to approach a speaker later and say you liked their talk and are wondering about ____. This is also totally okay if you're just too intimidated to ask a question in front of a large group. Personally, when I've given talks and no one has said a word to me about it later -- or if all anyone says is the equivalent of "great talk!" -- I worry.
9. Know how talks get selected.
At least at the academic conferences I go to, program committees don't select talks based on presentation quality, because they don't get to see the talks first or figure out how good a speaker the presenter is (in fact, often they don't know who will speak, because papers usually have multiple authors and only one will give the talk.) They select talks based on their assessment of the quality of the papers that go with them. Selection also isn't an objective process; political, messy, human one (just ask anyone who's been on a PC). Inclusion in a given conference, even a conference with a good reputation, doesn't imply lasting value. Rejection doesn't imply absence of value.
I'm saying this to encourage you to go easy on yourself if you miss talks or don't get much out of one or many talks. It doesn't necessarily mean that you had a great opportunity to learn something, and you (and only you) squandered it. When choosing talks to go to -- or choosing how hard to listen! -- trust your own judgment and don't assume everything is a pearl of wisdom.
10. Know that sometimes a great idea is buried in a bad talk.
Even if a talk leaves you reeling and not in a good way, maybe it just means you should read the paper. Different people learn differently, but for many of us, it's easier to understand something when we can go back and read the same sentence six times before continuing. You can achieve something similar by re-watching the video (if you're at a conference that records talks) later, which also has the advantage that you can rewind parts you want to listen to again and fast-forward through parts you don't. All of this only applies if the idea actually interests you. There's no obligation. In my experience, the most common scenario is a terrible talk based on an alternately lucid and confusing paper about a cool idea.