If you actually want to do something other than choose between the two options presented by the two major parties on election day, then your ONLY real option is to get involved in the process at a MUCH deeper level.

That starts with voting in primaries...and voting for lesser elections...but it also involves actually getting involved with one of the two major parties at a local level and doing more. Supporting candidates you like from the ground up, perhaps even running as a candidate for some minor office if there's not enough competition, attending meetings and otherwise getting genuinely involved with the political process.

Because voting third party in the US on election day has no more meaning than not voting at all. Third parties are not viable in the US system, and never will be. The choice will always be between two at that point, so the only way to improve is to get into it earlier in the process.

If you don't do that, then all you can do is pick between Republican and Democrat and that's it. Doing anything else is not participating, it's pretending to participate. It's showing up to a game of poker and declaring your 2 aces as blackjack. You're not playing the game that's being played if you do that.