Change the key violations to 5 seconds, not 3, but make them enforced strictly as opposed to not at all.
Change the goaltending rules to the European / international variant.
Enforce suspensions for flopping and foul hunting. Trae Young would have played a lot fewer games this year.
Remove all the nonsense technicals we see in today's game. Tying in with this would be bringing in a wholly new generation of officials, given the zombies we've been stuck with for decades. Would also try to enforce rules being the same for all. What a rookie gets a tech for, so does LeBron.
Change the challenge system. If you win a challenge you keep your challenge and your timeout. One per half, and another given if the game goes to OT.
Widen the court, push the 3 point line to 25 feet.
Reduce the number of jerseys a team has.
Would also be interested in a 1+1 bonus like used in college basketball, at least until 10+ team fouls. Reward good free throw shooters, punish bad ones.