You could start with a lot more transparency. Everything that isn't critical to the defense of the nation should be public and auditable. Hot button issues like stock trading while in office, term limits and corporate lobbying could be fixed with simple laws if you ignore the whining of current office-holders. If you want to be more drastic, then start shifting power away from the federal government and towards local governments. Politicians who are close to their constituents are the only ones that can be sufficiently supervised. Reduce the role of the faraway central government to that of referee and coordinator and make sure that 99% of representatives time is spent in their own districts where the people can get a hold of them. Finally, if you want to flip the table completely then institute some form of sortition where another branch of government with equal power is formed from randomly selected citizens who are given the opportunity to represent their communities at the levers of power.