Vote
If you’re reading this, you're probably already planning to vote, but maybe the arguments below will come in handy if you’re trying to convince other people to vote.
Voting may seem obvious to some people, but to others it may seem obviously pointless. What good is one vote among millions? Even if you’re in a swing state, increasing a large number from n to n+1 seems unlikely to be worth the work required (assuming you will educate yourself about the issues and the candidates… or maybe even if you don’t; just the physical process of registering and casting a ballot takes some time).
The counterargument is that, if everyone followed the logic above, democracy could not function. It resembles the Prisoner’s Dilemma: any individual is better off not voting, but everyone is worse off if no one votes. To vote is to “cooperate” and to not vote is to “defect”. But in the classic Prisoner’s Dilemma, the prisoners cannot communicate with each other, which makes a big difference. When people can communicate, they can make an agreement: I’ll cooperate if you do. In some countries, voting is actually required by law (which makes some sense to me: what are laws good for, if not enforcing a universal agreement to cooperate in a Prisoner’s Dilemma?). In ours, it’s not legally required, but there is a social expectation, reinforced by education and PSAs: responsible adults should vote (preferably responsibly).
(In fact the same arguments may apply to every method mentioned on this web site.)
There are cases where voting seems especially futile. Presidential elections if you’re not in a swing state, for example. I live in one of the bluest states. My rationale for voting in presidential elections has basically been that it affects the published popular vote numbers, which affects perceptions. The effect is miniscule, of course, so it is arguably pointless. But there are often other races in the same election that are worth voting on (especially in the primaries), and I can’t help learning about presidential candidates and forming an opinion, so there is really no extra effort involved.