It's tempting to want to make it a privilege, e.g. you have to take an IQ test or a test of political knowledge & understanding to vote, but I think that would just end up being taken advantage of in a partisan way by politicians. So it should probably be a right for everyone, maybe even mandatory so that we don't have selection bias, e.g. an effect where a demographic with certain political alignment likes to vote more than another demographic. I also agree with everything else Zou said--ranked voting, let convicts vote, get rid of the electoral college, etc.