STAGE 1: The Approach
-you leave out some food for a wild animal to get.
-each piece of food makes the animal trust you a little more.
-eventually the animal starts following you around
STAGE 2: Building your Relationship
-It still isn't nearly fully tamed though, and it might start to wonder away from you
-it will follow you around as you kill things, feasting on your fallen foes, only helping when he feels he needs to defend himself.
-walking into a village or town might scare the animal at this stage.
STAGE 3: Having a pet
-after enough time following you around it will help you fight your enemies.
-the animal starts to hunt for you, bringing you food (depending on the animal you tamed)
-soon enough the animal is considered your tamed pet.
As for permanent Daedric minions, yes definitely. but summoning them should cause a penalty to the summoner (possibly health decrease, or having your health tied to the daedra (every 10 points of damage he gets, you get 2 or something)).
Same goes for Necromancers who want to raise some dead, but because the undead are relatively weak singularly, you should be able to raise a few with no penalty (or a small penalty and no penalty with a perk)