This list was written by Megan of Jezebel in her article, "Voter Suppression And You: A Guide For Unreal Americans" in Jezebel today. The full article details many of the current efforts by the GOP to disenfranchise Democratic voters. Don't let it happen this time!
1. Vote early, preferably in person. Most of the people who will be out and about to mount challenges will be doing this on Election Day proper. This also gives you a chance to makes sure you are registered properly and challenge back if anything is wrong.
2. Insist on a paper trail. Many states have this as an option now, but in some it's only upon request. Request.
3. Don't wear anything that signals your voting preferences. Some states have little-used laws that prevent "electioneering" in polling places, and there have been signals that the folks there to challenge some voters will be challenging people wearing Obama stuff. Leave it at home or in your car.
4. Bring picture ID. Your state may or may not require that you have it, but it is one good way to verify your identity and residency if challenged. If your address isn't up-to-date, many states can issue free temporary change-of-address cards, or just do the paperwork to get it officially changed today.
5. Stand your ground, politely. The point of a challenge is to keep you from voting, and they can win in two ways. The easiest thing to do — which is why they're doing it — is to embarrass you into leaving. Fuck that. If you can't win the challenge at the moment, demand a provisional ballot and a written explanation of what you need to do to make sure that it is counted. Speak only to official poll workers, and ignore the partisan hack if s/he tries to "help."
6. Ask for help. If there is a problem with your electronic machine, do not press done and leave the polling place. Insist that a poll worker help you until your vote is cast correctly. If it cannot be, tell them they need to request assistance from the appropriate authorities and refuse to leave or cast your ballot until the problem is corrected. If you leave, you've probably already lost. Do not forget to have a paper trail.
7. Ask for more help The Brennan Center For Justice, among other groups, will have lawyers on hand to take reports of problems and offer legal assistance by called 1-866-OUR-VOTE. Use it if you have to. Hopefully you won't have to.