Public funding of campaigns.
I would fix our electoral system to end first-past-the-gate voting. We could end the two party lock on our politics that we've created.
Ranked voting is my first choice as well.
Instead of the debates, which are a complete waste of time, I would require that both nominees and any viable third party candidate (if there ever is one) appear (separately) before both the House Committee on Ways and Means and the Senate Committee on Appropriations.
Gerrymandering needs to go. First and foremost.
Institutionalized fact checking. It would be a non-partisan body that would try to be as unbiased as possible while reigning in the wild claims of candidates. A centralized bank of ideas and truth. It would penalize repeating a lie.
I'd also love to see centralized government website that candidates can post their platforms and proposed budgets to. Featuring a direct comparison of candidates, and a function where you could plug in your own personal information and values and it would show how well the candidates align. It would of course need to be open source, and agreed upon by both sides to reduce bias.
Right this minute today, if I can only choose one thing it would be ending endorsements, I've spent more time watching the news cover who's endorsing or not endorsing who than hearing platform ideas... not that either had a platform they wanted to actually explain and talk about.
If I get more choices I also want to end the electoral college and go to the actual vote.
I'm not so sure the presidential election process is what the problem is. Look at what is to be elected upon today. The president is the by-product of a two party system that is now thoroughly corrupted by special interest groups, supported by lobbyists who in many cases are ex-government lawmakers. By the time a presidential election occurs, the best scum has risen to the top and that is what you are forced to choose, the less toxic of two scum. What needs to change happens way before that time.