1) Direct election of the President
Democracy is based on the principle of one person, one vote. The electoral system, however, assigns electors to each state according to their total representation in Congress, in which every state has a number of representatives fairly reflective of its population but also -- no matter its size or population -- 2 senators. In large-population states such as California and Texas, the addition of 2 does not greatly affect the ratio of electors to voters. In low-population states, however, such as Wyoming and Vermont, the addition of 2 effectively triples that ratio. In other words, a Vermonter's vote for President is worth 3 times as much as a Texan's vote. Since the 17th amendment to the Constitution in 1913, U.S. Senators have been directly elected. The President ought to be as well.
Further, because most states assign all their electors to the winner of their popular vote, votes for the loser in that state end up counting as nothing. A Republican, for example, in a consistently Democratic state essentially never gets his or her vote counted for President. (And analysts wonder why turnout is so low.) Until the anachronistic electoral system is abolished, states ought to at least assign their electors in proportion to the popular vote, so the electoral result is a little more reflective of the popular result. Maine and Nebraska do so already.
2) Instant run-off voting
Voters should be comfortable voting according to their true opinion rather than having to strategize their vote. The resulting winner should reflect the general desire of the majority. If, for example, there are 1 "conservative" and 3 "liberal" candidates in an election, the majority may vote "liberal" yet the "conservative" may win -- even though the majority would prefer any of the "liberals." Instant run-off voting allows the voter to specify a 2nd and 3rd choice as well as the 1st choice. If the counting of 1st-choice votes does not produce a majority winner, then the lower-polling candidates are dropped and the 2nd-choice votes on those ballots counted, etc.
3) Proportional representation
With the current winner-takes-all system in most elections for representative bodies, it is typical that more than half of the voters are in fact not represented in government. (Yet, again, analysts wonder why participation is so low.) Representation ought to reflect the opinions of all voters. The Center for Voting and Democracy describes the many ways such "full" representation has been and can be implemented.
[Also see "Is Mandatory Voting a Good Idea?"]