1-Replace the first pre-season game with a mandatory scrimmage between teams. Alternate years for teams to travel based on Conference. (eg. Even years AFC teams travel to NFC camps for scrimmage...) Open it to the public.
2-Hold two pre-season games in the weeks they are being held now. One home game and one away game.
3-Skip the last pre-season game in lieu of a "healing week". Give the teams a chance to watch the tape from camp, the games and scrimmages and a chance for players to heal up for the first regular season game. More of a chance to evaluate players.
4-Change the cutdown from 80 to 70 players after the first pre-season game. Have a cutdown from 70 to 60 players after the second preseason game. Cut from 60 to 53 the last sunday before the season starts.
I just think that the more time starters get to practice with each other, the better they will mesh and become one unit.