First, you need to ask yourself how many Talent Points will your pet have? Your pet gets one Talent Point at level 20 (regardless of whether you leveled the pet to 20 or not), and one Talent Point every 4 levels afterwards (again regardless of whether you leveled the pet to its current level). At level 80, that means 16 Talent Points.
But wait! There's more! Hunters who spec Beast Mastery are able to get the Beast Mastery talent for themselves, adding another 4 Talent Points for their pet (all of your pets get this).
The Talent Tree is split into 5 Tiers. In order to pick a Talent from any given Tier you must have picked 3 Talents for every level below it. So you need 3 Talent points in Tier 1 before you can pick any Talents from Tier 2; you need 6 Talent Points in Tier 1 and Tier 2 combined before you can pick from Tier 3, etc.
Talents have from 1 to 3 ranks, each rank requiring one Talent Point. The entire tree would cost 32 Talent points, but as 20 is the maximum you need to decide which Talents are not worth picking up.
In Tier One you have the following Talents:
- Cobra Reflexes, 2 Ranks. This Talent increases the attack speed by 15% and then 30%, but reduces the damage of each hit. The overall effect is to increase damage, but I am not sure what the effect of lower hit value is on threat. I do not pick up these Talents. -- Note: Rick in China (see comments below) has pointed out that the Pet's threat is actually increased with this Talent, so this is actually a good Talent for BM Hunters to give their Pets. In addition, the faster hits means that the stacking effect of Rabid (see Tier 5) happens much faster and more frequently.
- Dash or Dive (depending on pet type), 1 rank. Increases the pet's speed by 80% for 16 seconds. This will help in surprising ways. Not only does the pet get to the mob faster, it can get back to you faster if you have taken on multiple mobs at once and you are getting attacked. This has saved my bacon more than once, and I always pick this one up.
- Great Stamina, 3 Ranks. Increases pet's stamina by 4%, 8% and 12%. Since you need to pick 3 Talents in Tier 1, this may well be where you pick up the other two points, at least to start off with. The choice is between this Talent, which increases the total amount of Health your pet has, and choosing the next Talent, which increases the Armor and therefore reduces the amount of damage that your pet takes. -- Note: with the correction that I got about Cobra, I no longer bother with this, until I have nothing else good to pick in later levels.
- Natural Armor, 2 Ranks. Increases your pet's armor by 5%, then 10%. Since later Talents will increase some of the healing abilities of your pet, Great Stamina might be a better choice. You can fill in some extra Talent points here in later levels if you choose. -- Note: Again, Cobra appears to be the better choice, along with Dash/Dive.
- Bloodthirsty, 2 Ranks. Pet's attacks have a 5%/10% chance to to increase happiness by 5% and health by 10%. This is huge; I have only one point in this Talent so far and I rarely have to feed my pet anymore. The reasons this is so effective are a) your pet's happiness does not suddenly drop in the middle of battle, which would reduce damage by about a third; and b) your pet has a much lower chance of dying, and the mana cost of healing is reduced. This is one case where a non-DPS Talent radically affects DPS in a positive way. Plus, having points in this Talent helps later on with other higher Tier Talents.
- Boar's Speed, 1 Rank. Increases Pet's speed by 30%. This is of limited value in my opinion.
- Improved Cower, 2 Ranks. Decreases damage to pet by 10%/20% over the next 10 seconds. Bloodthirsty already benefits total Health, and I am not sure if Cower reduces threat, so I am not a huge fan of this Talent.
- Spiked Collar, 3 Ranks. Increase damage done by pet by 3%/6%/9%. Extra damage is good, so you will probably end up making on this.
- Avoidance, 3 Ranks. Reduces damage to pet by AoE effect by 25%/50%/75%. I can see having this Talent for pets to be used in specific raids. Other than that I am not crazy about this.
- Charge or Swoop (depending on pet type), 1 Rank. Pet charges or swoops an enemy, immobilizing it for 1 second, plus increases pet's melee attack power by 25 % on the next attack. The benefits of this are limited, I think, but consider this when using up extra Talent points.
- Lionhearted, 2 Ranks. Reduces duration of Stun and Fear effects by 15%/30%. This can be useful in certain situations; less time out of action means more damage by the pet, and less damage to the Hunter.
- Great Resistance, 3 Ranks. Reduces damage to pet by Arcane, Fire, Frost, Nature and Shadow Magic by 3%/6%/9%. This is a small amount of damage reduction to be spending Talent Points on.
- Heart of the Phoenix, 1 Rank. Requires 2 Talent points in Bloodthirsty (Tier 2). When pet dies, it respawns immediately with full health (10 minute cool down). This is pure gold. I don't know how many times this would have saved my bacon in raids. This is equivalent to a 100% heal plus a total reduction in threat, which in a raid is fantastic. Even in PvP or PvE it will come in handy. Make sure you get this.
- Spider's Bite, 3 Ranks. Increases chance of Critical Strike by pet by 3%/6%/9%. Since Critical strikes are approximately double a normal hit, it is almost the same thing as an increase in base damage. But the higher your critical hit chance to start with, the lower the percentage effect this would be. However, it does increase the frequency that buffs and other procs will occur that depend on Critical Hits. Definitely consider getting at least one or two of these, if not all 3.
- Call of the Wild, 1 Rank. Requires 3 points in Spider's Bite. Pet's roar increase party's melee and ranged attack by 10%, with a 40 yard effect, for 20 seconds. In a large group, this can be a large amount of damage increase, vastly exceeding what the pet could do alone. for raiding, this is a great Talent to pick.
- Lick Your Wounds, 1 Rank. Requires 1 Point in Heart of the Phoenix. Pet heals itself for 100% of its health over 5 seconds. This requires channeling, during which overall damage is reduced. With other Talents and Skills you should have enough to heal your pet without too much problem, plus Heart of Phoenix is a good insurance policy. No need for this one.
- Rabid, 1 Rank. Requires 3 Points in Avoidance. Pet goes into a frenzy, Increasing Attack Power by 5%. Successful attacks have a 50% chance of increasing Attack Power by an additional 5%, which stacks up to 5 times. Lasts 20 seconds. With a potential overall increase of 25%, this might sound good, but to me it is a small benefit that can be used only every 45 seconds (cool down). Think about this only if you are running out of other good options.
This Talent Tree works well with Hunters who have the Beast Master spec. The Hunter's damage will not be enough to overcome the threat generated by the pet, and the Hunter's talents will drastically increase the damage and other benefits provided by the pet. Hunters who have the Marksman spec may find themselves stealing aggro from their pet; but on the other hand they can do a tremendous amount of damage as well. In raids with a good tank the aggro will not matter.