Requiring a valid state ID# on absentee ballots is perhaps the single most important measure to prevent voter fraud. If properly enforced, this completely removes the subjective interpretation of signature verification from poll workers. The 2020 election saw a near-universal abandonment of any meaningful signature verification, especially in the more populated counties not just because many urban areas willfully ignored the cheating going on, but because the sheer volume was unmanageable so everything counted.
There must also be a total ban on drop boxes and ballot harvesting.