In addition to the obvious fixes like Ranked Pairs voting, I'd say we need a Constitutional amendment bringing back independent agencies with their heads being directly elected rather than merely picked by whomever wins the presidential race. For example you shouldn't have to balance your guess of how you think one president will treat the ATF vs the NSF. Or the President shouldn't have any power over the Attorney General, as it's the Attorney General who should be prosecuting a criminal President, rather than merely being a lapdog in the criminal conspiracy. A race for each agency would also create focus on each agency head's actual results, rather than how the current guy is using a round-robin of all these different departments to create a tough-looking spectacle in one area, only to move on to another one when the actual results start becoming apparent.
We also need the right to recall for all national politicians, for obvious reasons.