Currently the United States uses a First Past the Post (FPP), winner-takes-all voting system.
FPP leads to tactical voting, wasted votes, gerrymandering, spoilers, and two-party systems. It also discourages the participation of third parties by making them a non-viable option through the above effects, forcing the people to vote for the "lesser of the two evils" rather than a party or candidate that they truly agree with. This in turn makes people apathetic about politics and less voters because there aren't options that they agree with.
I suggest having an Alternative Vote, or Instant-Runoff Voting (IRV) system instead. With IRV, voters can choose more than 1 candidate, in order of preference, rather than choosing just 1 candidate. This allows the public to vote for what they want.