If you haven't done so already, please register to vote. Here is a good place to start if you're new to voting - U.S. Government Register to Vote.
You also have the option to vote before the actual election day, for that you need to contact the state you live in for their early voting procedures. But remember, when you vote early you cannot change your vote for any reason. Not even if the person you voted for dies before election day. That would be a sad day of course but unchangeable nonetheless.
Register to vote! Every vote counts!