1. Uniformity of voting method, one which employs paper ballots. No more different voting machines at different areas within the same state. No more electronic machines with no paper trail. Ideally no more electronic machines at all (too many issues, too difficult to use, too many unqualified operators).
2. States submit their voter registration rolls to the feds for citizenship verification. Eliminates the need or desire, such as we see in Florida, for 50 individual states to be raiding various federal databases at will.
3. Uniformity of ballot. During a national election all ballots use the exact same style and format. Remember the Florida butterfly ballot -- which almost without question robbed Al Gore of the 2000 election. Sample ballots are published in newspapers nationwide well before an election. Due to complexity in some states (number of issues on ballot), prepare three separate ballots to be cast -- federal, state, local.
4. One-time registration to vote. Once you are verified, being stricken from the rolls for inactivity (as some states do) is an impediment to voting. As is being stricken because you are likely to vote Democrat If you've moved, but bring updated ID, I can't see any reason that can't be updated on election day. Let's make it easier to vote, not harder.
5. Depending on privacy issues, a nationwide database of those who voted in an election -- or at least a nationwide crosscheck for use by election officials. This would assuage any fears of multiple votes (which probably don't exist outside a handful of instances, but we have to throw the right a bone ).
6. Standardized early voting. Whatever is decided, make it uniform across the country, and permanent (Florida keeps diddling with theirs, trying to either restrict voting or confuse voters).