One thing you can do is try fighting monsters with Aspect of the Cheetah on. This is something I used to enjoy as it helped me kite better as long as I didn't get hit, but then if I did get hit it was a clear pointer that I had timed something wrong and needed to learn from my mistake. I also used to play around with how many enemies I could safely tackle at once, now including using the Freezing Trap and all my pet control skills I had been building up. Taking on monsters high above your level is always a fun change too, just to see how much you can get away with.
Probably the most annoying problem with leveling a hunter at this stage is that you'll be running out of mana a lot. You've probably already noticed this at earlier levels, but now your mana inefficiency is starting to disrupt of your hunterly groove. The only answer to this is: too bad. In my case, I just bring lots of water and drink liberally. Others may prefer to just kill enemies off more slowly with the pet and Auto Shot alone in order to save mana. Whatever you decide to do, get used to it, because it's going to get a lot worse as you continue to level up. If you want to use all your shots every fight, you'll be feeling the pain until you get up to level 64 and learn Aspect of the Viper.
Level 20: Aspect of the Cheetah is fairly obvious, and we've already covered Freezing Trap in the crowd-control section, but there's another new spell you learn at level 20: Disengage. It's not a class-defining ability, but it's helpful if you are really lazy with your threat management. If you're really learning your class well, however, your goal should be to use it as little as possible.
Level 22: Scorpid Sting might be handy on high-level enemies which seem to kill your pet before you can kill them, but really it's more of a group utility spell you can use to help out the tank in an instance. For that purpose, it's quite nice, but if you stay on your own most of the time, you'll be wanting to stick to Serpent Sting.
Level 24: Beast Lore is supposed to help you with finding new pet abilities out in the wild, but really it is far inefficient compared to other tools out there, such as Petopia and Fizzwidget's Hunter Helper, which tell you all the information you need to know without having to cast a spell on every animal you see. Besides, by this point, you should already have some sort of plan (based on those two resources I just mentioned) for how and where you are going to upgrade your pet and its abilities. If Beast Lore came at level 10 or 12 it might be a bit more useful, but by now you're already in the habit of getting by just fine without it, so it's hard to even justify putting it on your action bar. Just about its only use is for estimating the strength of an elite beast enemy, of which there are pretty few at this point. Besides, you shouldn't need exact numbers on their health and damage in order to beat them -- just send the pet in, attack, mend the pet, attack, win, and loot.
The other ability at this level, Track Hidden, is pretty nice for PvP. Until you get Flare, this is your best ability to help against rogues, if you're into twinking or PvPing as you level up. You can switch around between your various tracking abilities pretty often in order to get a good sense of what's going on around you without having to actually see it.
Level 26: Track Elementals, on the other hand, is just a random tracking ability you'll use now and then when you come up against elementals and want to see them on your minimap.
Rapid Fire is a bit more interesting. This is your first significant cooldown ability, and it's worth getting in the habit of using it at the beginning of a fight as often as you can in order to speed things up a bit. You can save it for a bit if you think a difficult fight is coming up, but otherwise you run the risk of never using it at all -- definitely a bad habit.
Level 28: Frost Trap is another more PvP oriented ability. It can help a little bit in PvE if you are trying to practice your kiting maneuvers, but it's main use is in the battlegrounds, where it can help slow down rogues and warriors in group battles. You can force them to run back and forth over the trapped space, slow down pursuers and flag carriers, and so on.
Level 30: Finally, you reach a landmark stage. Feign Death with save you lots of trouble, and in patch 2.4.3 you will be able to mount up at this point as well. Your talents also yield your first interesting talented ability too, but that's a discussion for next time.