When your first set of Augmented Reality glide challenges becomes available, do them for a very useful grappling hook upgrade.
The only immediately useful upgrade you can get is the one that slightly slows time when your freeflow combo hits x12, everything else you can get when you feel it's necessary.
There are easter eggs everywhere and some of them have achievements for finding them.
When the game is over, you'll get to go back and get anything you missed.
If you see one, find some place to see the whole thing and tap the Detective Mode button.
Riddler's hidden question marks are back.
You can't get every Riddler trophy you come across right away, you might have to come back with a new gadget.