This isn't a complete list of information, but here are a few things that I'd say if someone asked me 'what is something you wish you knew when you first started out playing prot?'
These points are in no particular order and typed out somewhat hastily.
- Learn your thunder clap radius. It can be really helpful when gathering up lots of mobs very quickly - with TC, you don't have to be turned to or directly targeting a mob to pick it up, particularly if you're with a group that is able to restrain themselves from blasting all their DPS cooldowns as you take a few seconds to gather.