Always save food for your pet

Pet Food
Always save food for your pet. You can see what types of food your pet eats by trying various foods, checking in your pet menu (hit C then select the Pet tab), or by checking in the Stable. Beast Lore can be cast on animals to see what types of food they prefer. You can also ask guild members and friends to save food for your pet and mail it to you! Awww how cute...

Pet Size
Pets scale to appropriate sizes. If you tame a pet, it will likely be smaller than the "monster" version. This was done because certain pets were very messy to play/group with at their default sizes.

Pet Customization
Passive abilities that are available include increased armor, stamina, Fire resistance, Frost resistance, Nature resistance, Shadow resistance, and Arcane resistance.

Pet Untrain
Hunter pets can be untrained of all their skills from any beast trainer in the major cities. Similar to talents, untraining a specific pet scales up as you do it more times: 10 silver, 50 silver, 1 gold, 2 gold, 3 gold, etc., eventually stopping at 10 gold.

Pet Experience
Hunter pets gain experience based on the level difference between the hunters, the pets and their target. Keep in mind that the Hunter must kill creatures from which he/she will gain experience.

Stables
You can house your pets at the Stables. Stables are located near Inns and Mailboxes. You can buy additional slots to contain more pets. If you want to switch pets and still keep both, do so at the Stables.

Pet Abilities

Beast Taming - Lets the hunter tame different pets.
Call Pet - Summons your pet to you.
Beast Training - Lets the Hunter train its pet with various abilities that it has learned. This opens up a menu where you can check out all of the pet abilities you've collected. Collect more pet abilities by taming different pets. You can then teach them to other pets.
Dismiss Pet - Dismisses your pet. Dismissing your pet will reduce its happiness by X.
Revive Pet - Revive your pet, returning it to life with X% of its base health.
Mend Pet - Heals your pet for X health over Y sec.
Pet Tips

If your pet is about to become very mad and you don't have food for him, put him in the stable until he cools off.
You can tame many special/cool animals out there. Go find them!
Pet Training

You can take the abilities you have learned from some pets and train them to other pets. The idea is that you have a main pet and other pets you use to gain abilities. You teach these new abilities to your main pet until you have what you want.
Other Pet Information

Base pet speed is standardized for all pets, including legacy pets.
All hunter pets will always deal Physical damage for their base attack.