1. Move the NFL Draft up from mid-April to mid-March to give more time for the league to practice and play.
2. Make it a legit NFL farm league. Each NFL team has one "JV" squad that participates in the league. Teams wear the same colors and uniforms as their sponsoring teams with some minor changes to distinguish between the NFL team and the D-league team. Maybe no/adjusted helmet decals.
3. Don't start right after the Superbowl. Both the AAF and XFL made this mistake. It's too soon.
4. Training camp starts and runs through April. This gives UDFAs a chance to be signed by teams.
5. 8 teams per division. Eight divisional round-robin games through May and June. Division champion goes to the playoffs.
6. Four team playoff centered around the 4th of July timeframe.
7. Players can only play in the league for four years. Once their time is up they move out to make room for incoming talent. If you have more than 3 years of experience on an NFL team you aren't eligible for the league.
8. Season ends mid-July which gives time for players to rest and be called up to the NFL team for August training camps.