|Services|| Follower |
Lydia wears heavy armour automatically, provided it is placed into her inventory and it is more powerful than her default armour. So a Dwarven Armor set that has been improved and enchanted is ideal early on, later Nordic armour or Ebony armour should be preferred.
Apparently Lydia has no affinity to magic, but will use staffs, as well as bows. Interestingly her default weapons are a sword and a shield, so providing better versions will be used readily, but even an enchanted greatsword or dagger will be used.
Should the Dragonborn buy land and build a manor, e.g. the Lakeview Manor, and not yet have a housecarl tending the residence (i.e. the Dragonborn is not yet Thane of Falkreath), she will offer to take on the job as a steward.