These are just my ideas based on what I miss on F1 compared to the 1990s-2000s when I watched it a lot. No idea if anything would even be achievable.
1) Less races, but more interesting tracks.
Tilke's tracks are just boring, they all follow the same formula. Go back to tracks that naturally wind through the landscape. Including Zandvoort ist a step in the right direction IMO.
2a) Make it more affordable.
That needs some balance tho. F1 always was an engineering contest to see what new and exciting ways to go faster can be thought up, and I get that. But F1 needs to be affordable enough so privateers and smaller manufacturers can join the sport again. Seeing Mercedes dominate year after year just because they can throw the most money at their F1 team is boring.
2b) Make it more affordable.
Circuits need to be able to afford to host F1 races, and that means the ticket prices need to be low enough so people can actually afford to spontaniously go to a F1 race. If it costs you several hundred Euros you're only attracting the hardcore fans, and those numbers are dwindling.
3) More charismatic drivers.
Let the boys be boys again. Don't stifle their personalities by corporate bullshit. Let them be toxic if they need to vent. The sport needs personalities, not drones who aren't allowed to talk from their hearts. Example: There was a segment a few years ago where Hamilton met Moss at Silverstone. It was some kind of Mercedes PR event. When they asked Moss about Silverstone, he was like "Oh it's lovely isn't it? I like being here, you meet some great people, sit on the balconies and watch the cars go by etc." Hamilton was like "It's great to be here and I'd like to thank our Sponsors and you guys at home, you make it all possible bla bla". EMPTY. There is no visible passion for the sport, it all seems to be very sterile. They're all the same. We need great analytic minds like Prost or Lauda compared to the playboys like Moss or Hunt, and the odd legend like Senna.
4) Entertainment value.
Make the cars loud again. I'm not saying bring back V10s, but try to make the current engines sound like F1 engines sounded for decades. Even tho V6 Turbos in the eighties sounded better. The Porsche 919 is a Hybrid V4, and it sounded way better IMO. Make the cars smaller and more nimble. Reduce aero to a point where you can go bumper to bumper without losing all of your cornering grip. Less aero means you can do away with DRS. Eliminate the need for the driver to fumble with fuel maps and ERS deployment maps. Set those in the beginning of the race and maybe allow a changes at pit stops, make them part of the strategy. Let the driver concentrate on driving his car.
5) Less bureaucracy.
I understand that there need to be rules and oversight, the question is when its too much. I have hopes that the current gouverning body is open to make things a bit less strict. Maybe thing like allowing the teams to use different engine configurations, like LMP1 did. You have an engergy budget per lap you can use. Bigger engine means less hybrid power and vice versa. Maybe even allow teams to not use Hybrids at all, and try to balance the different engine types against each other.
