1) No rider to bills. Bills should be about one specific issue of legislation, and nothing more. I think there is a valid point that bills are too long, it makes it easier to hide a tiny little bullshit exception and loophole. By making laws more specific, it makes it easier to know what the law intends to do, what it does, and so that stuff no one likes cant' be added to a bill to make it pass. I'd also say we should think about an amendment to allow Line Item Veto's by the President, but I"m on the fence about that one.
2) Campaign finance reform. The amount of money in our election process is disgusting, it's obviously corrupting, and it has made the election a constant pressure, a constant concern. At the very minimum, we need to drastically reduce individual contributions, and ban corporate contributions (corporations are not people, as obvious as that should be), but there are some models that use basically tax credits to finance elections. That means each and every person can contribute, but only up to a certain amount, and is essentially publicly financed. Not only would this help
3) Basically, end lobbying as we know it. No institutional lobbying, no professional lobbyists. All lobbying serves to do now is corrupt the system, and make legislation corrupt and more interested in a couple of persons private interests over the general public good. Social media is more than capable of bringing important issues to the national stage, regardless of how "big" the issue is. There's also a non-corrupt way to inform legislators of the consequences of their proposals.