Loot rules are pretty simple these days, seeing as how personal loot is mandatory, but there are still a couple of things you should know before raiding with us.
First, if you get loot, congrats! If it's an upgrade or you just can't trade it then there's nothing more that can be said.
If you don't need something and you can trade it to another raid member who needs it, you will be expected to do so. We all put in the effort to kill these bosses and it is therefore only fair that these items be traded rather than just kept for scrap. If no one needs the item then it will be disenchanted and the mats put in the bank for all raiders to use for raid enchantments.
Items needed by multiple people will be rolled for the old-fashioned way, with the old loot priority still in place (Advocates first, Trials second). We could theoretically still use a DKP/EPGP system to decide who has priority but this is more difficult to manage than you might think, and not really worth the effort.
If you get a cosmetic item drop (pet/mount) then it's yours to keep, unless you already have it or are just feeling generous.