Several:
Pay for College like we pay for Social Security. You get the college education/technical training up front but pay for it over your working life (and a few other reforms). Thus costs is no longer a barrier to acquiring trades, going to a university, or just improving your self for the sake of improving yourself (for example, taking Italian language classes so when you visit Italy, you will be able to converse in the native language).
Remove the power that the State legislatures currently have to draw congressional districts. In our system, you’re supposed to select the candidates; what is happening is that the candidates are selecting the voters.
Replace it with a mandatory lottery system based zip codes or area codes or some other non-political designation. Divide up codes/precincts/territories/etc… into equitable population sizes and assign them to each district at random. So in 2020 for example, the SC-1 district may have zip codes from Hilton Head, Columbia, Greenville, Myrtle Beach, and Savannah. The SC-2 may have zip codes from the same cities. In 2030, those districts may have completely different constituencies as reapportionment happens every 10 years.
Use the states as laboratories on the federal level. For example, if you want to see if a medicare-for-all system is workable, take 10 states and try that system in those 10 states for 5 years. See what the results are at the end and use that as a benchmark to see if medicare-for-all is workable. Do this with background checks, pollution laws, welfare reform, etc…
First and foremost, probably though, you need to pop the hood open on the Constitution to add voice to it where it currently silent. The blob has shown us what a president with no regard for the law can do when the constitution doesn’t expressly forbid it.