Learn the chants!
There are a few different moments during the concert where the crowd chant something ahead of / after one of her lyrics, so it seems like an interaction.
So for Delicate, which is in the reputation era portion, near the start of the song she sings "I know we can't make any promises now can we, but you can make me a drink" and the crowd shouts "1, 2, 3 let's go bitch!".
Look then up on YouTube, you'll find all of them there.
You can find the set list as a playlist on Spotify or just look it up online, so you know what the songs are - it's definitely worth listening to the set list tracks if you don't know all her music. Although as she has just released two new albums, there is a good likelihood the set list may change, so if you wait until she's done the first few shows of this new leg of the tour, you should be able to get the updated version.
Also worth looking online at bathroom breaks - swifties have info online about where the biggest gaps are for set /costume changes so when your best bet for going to the loo will be, without missing any of the show.
Definitely, 100% you need to learn the first bridge in Cruel Summer as the whole stadium will scream it (I'm drunk in the back of the car, and I cried like a baby coming home from the bar, said I'm fine but it wasn't true, I don't want to keep secrets just to keep you! Etc). Also make sure you've listened (and learned!) the ten minute version of All Too Well, because, again, the crowd will sing/ scream that whole song so it will be an amazing thing to be a part of.
Friendship bracelets for trading, has to be done.
Glitter, sequins, sparkle. All of it. As much as possible.
I'm going in June, can you tell I'm excited?!? 😃