Ask a manager has a recent post requesting tips for young professionals attending their first conferences, and the post has a long list of good suggestions.
I've gone to a bunch of conferences in grad school and for work. A few of my suggestions (most of which were already covered):
1. Have a sweater or other warm cover-up such as a suit blazer, and make sure you have a respectable enough underlayer that you're comfortable taking the outer layer off. Expect the temperature control to be all over the place.
2. Comfortable shoes!
3. If you're going with other coworkers/students, divide up the sessions in advance so that you get more out of the conference as a group. The "in advance" bit is important because otherwise you'll spend all the time between sessions brainstorming who's going where.
4. If you're going in a big group, try to split up so that you don't default to hanging out only with the folks you already know.
5. If you don't know anybody at the conference, remember that you can always buttonhole the folks who have given presentations you've seen - you already have at least one topic to discuss.
6. Have a handy, easily-reachable place for business cards you receive, and one for your own business cards. Keep these separate, so you don't have to shuffle through other folks' cards to find some of your own.
7. I always try to wear shirts/tops with either pockets, buttons, or something else that I can clip my nametag on without having to stick it next to my neck or down by my hip.
8. I like to bring a thin bag that's big enough for my personal stuff and has some sort of dividers so that I can keep my conference swag and my notes separate, such as a small laptop bag.
9. Don't be afraid to ask questions! Presenters, organizers, and vendors are all happy to chat.
I always enjoy conferences - you get to meet a bunch of folks who are doing similar things or are at a similar stage in their career, but who live all over the country. And if you're lucky, you may find the perfect research method/product/client/employer while you're waiting in line.