1: Keep her personality the same as it was in the Tracey Ullman Shorts instead of making her a stereotypical smart character that no one asked for
2: Discipline her some more and not make her a Mary-Sue, like punish both her and Bart in Bart vs Thanksgiving instead of just Bart
3: Don't ever make her a Vegetarian, because that was the reason why Lisa was flanderized and a bad character since Season 7
4: Not make her Jealous because of how dangerous it is, and it resulted in her turning into a villain since Season 14
5: Not make her a Buzzkiller nor annoy the audience
6: Have her crush be Nelson but make it Permanent, and not have her be in love with other people
7: Make her remain as a Troublemaker like Bart
8: Not make her a feminist, nor have her make that feminist centerpiece
9: Never have her smart nor intelligent because it was a bad idea to portray a fictional character like that in the first place
10: No Sympathy arcs, nor make her a Karma Houdini
11: Remove episodes like, Lisa the Vegetarian, Lisa the Simpson, Dude Where's My Ranch, On a Clear Day I can't see my Sister, Bart vs Itchy and Scratchy, Lisa Goes Gaga, etc.
12: Not make the writers have her as their political soapbox
13: Not make her a SJW
14: No making her a Buddhist
15: Not cause any unforgivable things such as sabotage, murder, selfishness, etc.
16: Have actual emotional attachment from her rather than using it just for attention and sympathy, and in a snobby kind of way
17: Have her show some proper respect to her family rather than going against them
18: Even if she doesn't like it, have her still thank people for giving her whatever gift they made, rather than crying about it
19: Make her understand that the world doesn't revolve around her
20: Give her an actual sense of humor
All of these things would prevent her from being one of the worst characters, If not the worst character ever made. Matt Groening should've realized that it wasn't a good idea to change her personality back in 1989. And I don't want anyone thinking nor stating that I'm wrong, nor saying that these steps are terrible, and claiming that it's not how you fix a character. At least these steps are way better than her being the worst character in television history. I just wish that the writers could see potential in Lisa's 1980's counterpart, rather than changing it to try and make her more likable, but it failed. Tracey Ullman Lisa is pretty much the best they could do for her character. Her character has gotten worse once the series becomes a full animated sitcom in 1989.
And I apologize if I was going too far on what I said.