Graduate Student Handbook
Networking is a skill that most people have to learn. Just going to conferences and standing in the corner isn't enough. You have to make a conscious effort to meet and build relationships with other researchers. This is not always easy, especially if you're shy or not normally outgoing, but the rewards of using this skill well are huge.
Generally, any public speaking pointers are useful. Practice handshaking, direct eye contact, and remembering peoples names. Then introduce yourself to people whose presentations or papers you found interesting so that you'll have something to begin with. Have summaries of your research of various lengths and technical detail mentally prepared so that you can answer the inevitable "What are you working on?" intelligently and clearly. Talk about your research every chance you get, but be sure to hone your listening skills as well. If someone is interested in your work, be sure to get their name and e-mail address, and make a note to follow up by sending papers or asking for feedback on ideas.
If you're having a hard time just introducing yourself, ask your advisor or a friend to introduce you. Sometimes just gritting your teeth and jumping in is the best way to get around the shyness block--polish up your smile and memorize your research description and just do it! Most people are all too happy to discuss their research with an interested person. Talking to people just before lunch can often get you invited along--go! There are usually other contacts along as well, and the informal setting could help you relax. Try to avoid butting in on other conversations or catching a speaker just before they are scheduled to go on.
Meeting people is only the first part; maintaining these relationships forms the network in question. E-mail people whom you've met and let them know you're still interested. Reestablish contact at each workshop or conference you attend. Reintroduce yourself and use their names and a reference to let them know you remembered them. Some people even have business cards made up with research interests and e-mail addresses on them to help jog others' memories. If the opportunity for a collaborative effort arises, seize it! This will expose you to other methods and other groups of people.
Additionally, you may be called on to speak with the media about a mission you are involved with, or about your really cool science. If so, the AGU has created a handy Media Guide in Adobe PDF format that may help you deal with the news media in a professional manner.