This advice cannot be overstated. I'm a poll worker, and I can say that even when a person is permitted to vote without timely pre-registration, that vote will not affect the election outcome.
strea3mTo register to vote or to check that your registration remains valid (do this check repeatedly, especially as the midterms get closer): Go to the website for the Secretary of State for your state, and use the voting related options as needed. Find yours here www.e-secretaryofstate.com