I know it is a cliche', but I am going to say anyway what you already know. Vote. It is important.
Lots of folks have died to give you the right to vote. Lots more have died in other countries for want of what you have, the right to have your say. Vote for them. People you have known and loved in your lifetime were excluded from the right to vote because they weren't white or weren't male. Vote for them.
People, including the military and the foreign service, are STILL serving, STILL sacrificing, STILL dying, for your right to vote. Twenty-nine years ago today, on November 4, 1979, a group of Iranian students took over our embassy in Tehran and held 52 diplomats hostage for 444 days. Those diplomats were serving for you, serving you and your right to vote. (You can read more about that and see the names of the hostages on Diplopundit.) Vote for them too.
Even if the person you support doesn't win, honor the fact that you get to have a say because so many have fought for it before you. Please don't throw that away.