US Citizens! If you aren't registered to vote at your current address, make sure you are! Deadlines for some states have already passed, and others are rapidly approaching. (I need to mail mine in before 10/15. It's been in my bag for over a month, for want of a stamp. Yes, very delinquent of me.)
The most important thing is that everyone votes. I know not everyone reading this will agree with my political opinions, or vote for the same people as me, but you should vote!
Also, make sure to research the candidates running for Senate, House, and lower levels, and to consider any issues that will be on the ballot. I know MA has three questions this year, and I already know how I'm voting on them.