I would say stop the partisan politics. All the bickering just makes the nations Capitol look like a kindergarten on a sugar overload.
If the United States wants to be a world leader then it should set an example to the world. Bickering sends out the wrong message, it says we are weak at home.
Get the balance right and looking like a leader that can solve it's own problems will do wonders.
As for policies I would say clean up the health system, make education a REAL priority and invest in schools not just blame them for the nations problems.