1. Let them fight
If your going to call it Batman v Superman and take elements from The Dark Knight Returns,then it's only going to anger off people if you don't answer the age old question of who would win a fight Superman or Batman(also compare Supermans and Batmans feud with Zeus,a God who embraced his destiny and Promethues,a Champion of the people but doesn't want to take in the glory.) And since in Man of Steel,Superman and Zod while fighting caused damage unintentially of course but I imagine it would be interesting how they could come up with a way for Batman to stand up to him.
2. Superman needs to lead this movie...and win the fight.
After Man of Steel the reason why I loved that movie so much is because it opened so many opportunities Terrio/Snyder can go with Superman and the DC universe,Zods invasion was not only the reveal of Superman to the world, but the reveal that there is gods living among them to the public(I assume the government and Batman and Lex already knew before Superman arrived because why would the government reveal that there's an island full of amazons or the underwater city of Atlantis? It would cause panic). But because this is his movie,it has to focus on Supermans development into a hero or if some time passed then show how he's different than what we saw him before. And finally on this topic the reason why Superman needs to win the fight because he needs to show Batman that he is not a threat and he wants to help.
3.The interaction between the duo.
This is the unique selling point, you need to show valuable screen time of the development of them as enemy to friend.
4. Lex should not go after Superman....yet.
After Man of Steel,there is plenty of reason for Lex to just make a Superman clone or Doomsday and just send him after Superman to kill him. To which I say no because Lex is a mastermind,he's very smart. He would not go for the direct approach. Rumors of KGBeast in Batman v Superman and a rumor that there was a funeral for the president opens up new possibilities, like Lex hiring KGBeast to kill the president so Lex can be up for re-election.if he wanted,he could frame Superman and that's what causes Batman to hunt him down(that sounds like Terrio to me). After Lex becomes president then he'll have the whole support to build Doomsday.
5.Give Wonder Woman a significant role but leave the rest of the DC heroes as cameos.
Because how big Zods invasion has caused, it will attract attention from others, and that's why I think BvS needs to establish is the world AFTER the invasion. After World War 2 the United nations were formed to make sure that doesn't happen again, I think the Justice League will be formed as a response to that invasion. But because this movie is focused on Superman first Batman second, it had to be from their P.O.V. Don't show plot points that you are not going to fully address until Wonder Woman or Aquaman movie.
and there you have it,if you have any other things you want in BvS that I didn't mention, comment below and a Merry Christmas and a Happy New Year.