1. Preferential voting rather than first-passed-the-post, which is an idiotic system designed the maintain the status quo; and
2. Mandatory voting. The level of voter suppression in the US is simply staggering.
But having a multi-party system doesn't really solve anywhere near as much as you might think. Other countries have this. Israel being one. And there you have single issue and single interest parties who hold a disproportionate sway because they only care about one thing.
In Australia at times we've had a small party (2-5 sEnators out of 76) who hold the balance of power and whatever pet issues they have have to be addressed, which is fine if you agree with them but not so fine if you don't. In times passed this has included the Australian Democrats (whose bargain with the Howard Government to pass GST also led to the downfall of the party in big part) and the Greens. But it could just as easily have been One Nation, a dog-whistle anti-immigration, pro-White party that looks like a real "pioneer" in the Trump era.