1.) SCHEDULE. Most conventions make their schedule available on line in advance. Check it out, make a penciled-in tentative plan, but be open to the idea of erasing them. If there's a must-see panel, mark it as such, but leave yourself some room before and especially after in case you have an opportunity to hang out with some like-minded folks you met in the panel. Cons are about opportunities and, as Jeffe said, meeting people and engaging them in conversation.
Techy sidebar: The fabulous DragonCon even has a free app for your smart phone. Through it you can get the schedule--which you can search by topic/track, by time, or by speaker. It also includes info on dealers, maps, etc., and gives you the option to make notes about whether or not you liked a panel and why.
2.) REST. Sure, you want to be a part of the up-until-4am-crowd, guffawing in the lounge. Just don't have plans for breakfast with someone important, like an editor, at 7:30. (Unless they're in the lounge with you...) You want to be at your best for certain meetings you may have scheduled. You don't want to crash hard at a bad moment because all the partying caught up with you.
Medicinal Sidebar: Me, I don't sleep well in hotels, so the Tylenol PM always gets packed to better the chances that I sleep. And if the mid-afternoon isn't hoppin', I might sneak off to my room and take a short nap.
You may not be doing much more than walking around a bit, sitting through panels, and chatting, but you will be exhausted when its over. You are mentally ON the whole time, and that is wearying. (Or I'm getting old.)
3.) SHOES. I've been stupid about this. NO MORE! I know what's best, and what's doable. There are plenty of awesome shoes that won't distract your focus from what you came to do.
Been-There Sidebar: Don't even pack the 'I'll tough it out' pair of heels. You won't. No matter how awesome those shoes are. You'll end up miserable, whiny, and barefooted with street dirt between your toes, or both. Don't be stupid.
4.) REMEMBER YOU CAME TO LEARN, MAKE NEW FRIENDS, MEET SOME INDUSTRY PROS, AND HAVE FUN.
Seize the moments so you can check all those off your list.
Pep-talk Sidebar: Demand self-action. Do what you came to do.