Levels 10 to 14: 5 points -- If it's your first time leveling a hunter, I suggest putting your first five talent points in to Endurance Training, so that you and your pet get that extra edge in survivability, especially when going up against tougher monsters and trying to do quests you wouldn't normally be able to do on your own with other classes. If it's your second time leveling a hunter, though, try and mix it up a bit. Improved Aspect of the Hawk is a nice talent, and it's fun to see it go off now and then, even if it doesn't have all that much impact on your damage.
Some people say that Hawk Eye from the Survival tree is extremely useful for hunters at all levels, but to me it's better to focus on the talents in Beast Mastery, so that you can get the more advanced talents sooner rather than later.
Levels 15 to 19: 10 points -- Your next five points should go into Thick Hide and Focused Fire. Like Endurance Training, Thick Hide helps your pet stay alive while tanking for you, while Focused Fire provides a nice little dash of extra damage (as well as a buff to your Kill Command ability, which you unfortunately won't get to take advantage of for a long while yet). You shouldn't need to use Aspect of the Monkey so much that you'd need an improved version of it, and ideally you should also be learning to play in such a way that you don't need to revive your pet that often. On the other hand, you can't be perfect all the time -- some people like being able to use Improved Revive Pet as a backup for situations when things go bad, especially since Beast Mastery hunters rely on their pets so much. To me, however, it doesn't seem worth the loss of extra damage or extra armor for your pet.
Level 20: 11 points -- Bestial Swiftness is a very nice talent for leveling, since so much of your time will be spent outdoors, waiting for your pet to get to your target so you can open fire. It helps speed that up a bit, and it also helps in situations when enemies are running away, since your pet can easily keep pace with them.
Level 21 to 29: 20 points -- Skip Pathfinding at this point: more speed for yourself is always nice, but the daze effect on Aspect of the Cheetah means this isn't worth the tradeoff, and other talents are going to be much more valuable.
Go ahead and fill out Unleashed Fury instead. You'll be wanting your pet to do as much damage as possible, and this is the point when you start getting talents to really help with that. Don't worry about Improved Mend Pet just yet -- we'll be coming back for one point in that later. First, you'll want to get the first four points in Ferocity until you reach...
Level 30: 21 points -- Now you take Intimidation. This is a very handy spell for those situations where you need your pet to build threat fast in order to save your skin. It can also interrupt those horrible debuff spells monsters can sometimes cast on you just as they're about to die; some of these debuffs last 10 minutes or more and can be very annoying indeed. Intimidation is a great ability when you use it at the right moment.
Level 31 to 34: 25 points -- Next, take Bestial Discipline for the very noticeable increase in your pet's focus generation. More focus means more special abilities and more damage, which is always fun. Next, go back to Ferocity and get the last point there, and finally take one point in Improved Mend Pet to bring you up to a full 25 in this talent tree. You'll only need one point in Improved Mend Pet in order to remove the odd debilitating curse or disease that will afflict your pet from time to time. More than one point in this talent is hard to justify, especially in light of the other talents that become available once you have 25 points. On a side note, Spirit Bond looks nice, but in the end, 1-2% health every ten seconds doesn't amount to a whole lot -- certainly it is not worth the utility that other talents at this stage provide.
Level 35 to 39: 30 points -- Here there are several good ways you can do this, but this is the method I personally suggest: Take two points in Animal Handler so that your pet hardly ever misses an attack, and only after that start taking Frenzy. The bonus speed Frenzy gives your pet is quite nice, but to me it seems more important that your pets special abilities should hit more often. Besides, once you reach 3-4 points in Frenzy that should be enough to keep it up almost all the time. So for now just put 3 points in Frenzy and rejoice in finally getting to...
Level 40: 31 points -- Bestial Wrath is the signature ability that made Big Red Kitty famous. Unlike Intimidation, which you usually save for just the right moment, Bestial Wrath is best when you use it as often as possible. Obviously just try to time it towards the beginning of the fight so that every one of those 18 seconds of extra damage can be directly applied to your enemy.
That's it for now! By this point, your talents should look something like this. Later on, we'll come back to the rest of your talents as you progress past level 40, but for now these buffs and abilities are in themselves well worth looking forward to.