Preload Fighters Guild, Mages Guild, and Undaunted daily quests today; complete them but don't turn them in until you get your companions. While they're active when you turn them in each quest gives them half a rank and each character adds to it. With a roster of 18 characters you can get rank 10 to all 3 skill lines on the first day for one companion.
Assuming they haven't fixed the disappearing/duplicating gear bug for consoles in the update, when you equip your companion with a new piece of gear, Unsummon and Resummon them to force save their gear setup. Otherwise if you don't sometimes logging out and switching character can cause their new equipped item to be deleted and replaced with the item that was previously in that slot.
Starfall is an awesome ability in the Mages Guild line, its basically Meteor. I advise using as their first ability for two reasons:
1. It allows you to see what mob they are targeting to attack when combat starts or when they switch targets. This lets you somewhat coordinate with them, knowing what they're attacking when faced with multiple targets.
2. If you see the blue circle repeatedly spamming with no Meteor drop, it tells you the companion is not within Line of Sight and is unable to attack that target. They aren't going to move into position to be able to attack their target and will keep attempting to cast it until it hits, you have to move the target into visible sight for them to attack it.
Anyone have other stuff to add?