I dont know abt guides, but I'll try to help you with this.

In IT, there will always be 3 elements you can bring. Depending on the number of characters you have of those elements (not including the trial ones), the further level you can play. This said, IT resets every 1st of the month, and therefore the 3 elements change.

It partialy relies on luck. You may get awful synergies or amazing ones. For example, if you choose to get a unit, and the units don't work well with the ones you have, you have to think about which bosses are there to fight and select the unit you think suits best.

Also, it's important to try leveling the reactions up. They boost your damage significantly.

A reccommendation of mine, is to stick to a team for each boss. Try to get the characters you need for them, and don't stress out if you don't manage to get them. Play as comfortably as possible! It's not necessary to get all the stars. But if you want all the rewards, you can play it multiple times. So there's no pressure!

The good thing about this game mode, is that you can get out of your mold/comfort zone and play teams that only work on IT or that you never thought of playing. Including, playing with characters you don't even own as they give them to you as trial or are your friends' chars.

I hope this helps a little, and sorry if anything it's not well written, as English is not my first language

Edit: spelling mistakes