Not an airbus guy so can’t give you details but can give generic answer that will help you probably on any machine that moves by its power.
-Know your normal/non normal profiles, speed, pitch, thrust
-look at any switch/button/thing in the cockpit, tell yourself what is it for, how does it work, why does it work, thanks to which system it works, what happens if it fails. if you can’t, then read about it.
-know your memory items and non normal profiles like windshear/terrain escape, tcas, stalls, uprt
-checking and reading MELs/DDGs/CDLs can give you bunch of informations
-FCOM/FCTM anyways should give you the most knowledge you need (and a good way to fight insomnia)