The Hunter
1. Don't melee
2. Let your pet Tank Mobs
3. Use Freezing Trap to help with Adds
4. Use Scare Beast to help with adds when applicable
5. Go into Beast Mastery Talent Spec
6. Only get gear with agility and stamina on it
These are very simple concepts. Hunters do most of their DPS from ranged and you should never melee unless you are wingclipping an enemy, trapped, or afk.
Your pet is a mini-warrior angel sent from Blizzard to protect you, use it. Letting your pet tank and hold aggro will make your leveling smoother.
Freezing traps can help you with those group pulls of 2-4 mobs and so can scare beast. Use them both if you are fighting beasts but this will help you mitigate damage and keep your downtime to a minimum.
Beast Mastery is where it's at when you are leveling up. This ensures your pet does a lot more damage, can hold aggro better, and can tank like a champ so you don't have to melee or kite mobs.
Agility and stamina are the two most important stats for hunters. Sacrificing either of these for intellect or another crap stat isn't recommended because you will lessen your ranged DPS and survivability. It is possible to get away with agility/intellect as your primary stat but if you get into trouble it might not be pretty if you have low hitpoints.
The Hunter's Pet
1. Keep your pet happy and well fed
2. Train your pet in Natural Armor
3. Make sure you have a DPS Pet
4. Keep your pet's dps abilities updated (claw, bite)
5. Dash / Dive helps tremendously
Your pet does 125% damage when it is happy.
Your pet should have Natural Armor over Stamina and most other things you can train your pet to do that isn't, Dive/Dash, Bite/Claw/Gore, Growl. The reason for this is simple, your mend pet ability sucks so having more hp doesn't really benefit you much because it makes it harder to heal your pet, having your pet take reduced damage is vital to soloing. After I max natural armor I then go for resistances to reduce spell damage taken as well.
Make sure you have a DPS pet, don't let me catch you running around with a Bear, Croc, or some other stupid pet. The Owl has a +7% damage modification and can learn screech (an area attack that will help you hold aggro on multiple mobs) get one. If not, Ravager/Cat/Raptor are your other alternatives, don't let me catch you with anything else.
Dash/Dive lessens the time it takes for your pet to get to the enemies, this allows you to begin shooting faster. Don't forget to learn Bestial Swiftness in the Beast Mastery tree because this also helps.
Macros
1. This is the only macro you'll ever need below:
#show Auto Shot
/targetenemy [noharm]
/stopmacro [noharm]
/petattack
/cast Hunter's Mark
/startattack
This macro will select the nearest target, send your pet into attack, cast hunter's mark, and start shooting for you. It is the only one you need to level up in the game. You should be able to just run around and press it after each kill nonstop.
Game play
1. Don't stop killing
2. Don't group with anyone
You are one of the fastest killing classes in game with almost no downtime so don't stop killing because it's not necessary and slows down your experience.
Don't group with anyone, you are your own group (DPS, Tank, Heals) the only time you need a group is for an instance or possibly a group quest but you'll find you can solo some of these.
Addons
1. Recount
2. Quest Helper
3. Titan Panel
Recount to track how much damage per second you are doing, Quest Helper to help you level, and Titan Panel to let you know how much experience per hour you are getting. The only thing you need with these is a Leveling Guide so you can figure out where to go.
Additional Resources:
Hunter Pet Guide
Hunter Talent Guide
Hunter Leveling Guide
Hunter Pre-Raid Preparation Guide
Hunter Builds Explained
World of Warcraft Leveling Tips
All about Hunter Pets