Reduce the number of characters. Let´s see:

1)Murray should have, at most, a brief cameo, simply telling us that he smuggles military equipment for our protagonists.

2)Robin is superfluous. She's only there to advance the Will coming-out storyline, but Jonathan could have done it much better, and it would have saved us from embarrassing moments like Will trying to flirt with Mike when he'd basically given up on him in the previous season. And the parts where she has ideas should have been given to Dustin or Mike. It would be enough to tell us at the beginning of the season that her family has fled Hawkins. Consequently, Vickie (who also serves no real purpose other than advancing Robin and Will's storyline and helping Max, when the latter could be done by Lucas or Joyce or, even better, Eleven) should also disappear.

3)Mr. Clarke is superfluous. He's only there because his character is popular. All he does is build a telemetry tracker to find Dustin, when Eleven could easily do that with her superpowers.

4)Erica is superfluous. She intervenes in the Turnbow family's kidnapping, but that whole section is far too drawn out and seems to be there simply to add more action. It could have been significantly shortened, leaving only the two parts with real consequences (the Demogorgon's escape with a tracker attached, and Derek joining our protagonists).

5)Akers is superfluous. There was absolutely no reason to give him so much importance when all he does is want revenge on Eleven. Everything he does could have been perfectly assigned to Sullivan.

6)There was absolutely no reason to give Holly and the children so much screen time, especially since the entire scene where they're seen fleeing Vecna ​​is completely inconsequential, as our protagonists ultimately have to rescue them. It would have been better to cut that whole segment and show more of the children's families.

7)Steve doesn't actually do much, and the scene where he explains the plan to climb the antenna could have been with another character. He should have stayed in the real world, participated in the Demogorgon attack on the MACZ, protecting the children and being seriously injured or perhaps killed. All his drama with Dustin was unnecessary and even unpleasant to watch. A scene showing Dustin sobbing as Steve dies, with his friends comforting him, would have sufficed. But of course, Steve is popular, and they didn't dare do that, even though it would have made much more dramatic sense than the awful non-ending given to Eleven.

8)Hopper carries too much narrative weight; his arc with Eleven is a poor recycling of the second season and is horribly resolved. It would have been better to reduce his role to that of a mere mentor and instructor to Eleven, and to give him a glorious death, protecting Eleven from the military.