As a hunter, you should get to know that Kiting is one of the most essential skills in PvP. Kiting is where you maintain distance from a melee target while shooting at it. This is similar to "running and shooting over your shoulder". It works very well against classes that have poor or no ranged ability, since you can effectively kill them without them getting close.
At range, kiting is able to help Hunters do their best work and is relatively poor at melee. In most cases, a Hunter does not want to go toe-to-toe melee against a rogue or Warrior in that he will get slaughtered. Kiting allows us to keep our opponents at range.
Kiting can be accomplished in a number of ways. One is to jump in the air, spin at least 90 degrees towards the target (most people spin a full 180), shoot off an instant, and then spin back, all before hitting the ground. Thus, you are basically running in one direction while occasionally jump-spinning to face your target so that you can hit him.
Another involves using the strafe key to essentially run sideways away from the target. Done properly, you will still be slightly facing the target imperceptibly in most cases, so you can shoot your instants without having to jump and turn around.
That being said, it is important for you to learn how to kite at first may seem rather daunting. To jump and then spin, shoot, spin back, all before landing takes some work. Fortunately, this can be practiced against any landmark or inanimate target. You can for example choose a hallway in your town, then practice running up and down while jump spinning. Or, choose any stationary NPC in town and jump-spin with him as a dummy target.
But how do you to kite? We thing it a tricky thing so we talk about two hints for you. One is to learn how to jump-spin. When you first practice this, you may want to spin a complete 180 degrees. If you're having trouble spinning back to your original position, you may want to adjust your mouse. Another key thing to note is that as long as your mouse returns to its original position, you will also be back to facing in your original direction. Practice flicking the mouse and then flicking it back to the same horizontal position it started. You can even do this outside of WoW just by playing with your mouse on the screen. Once you can consistently flick it back to where it started, you're set for kiting.
Another is to watch your minimap. Since your minimap gives you an indication of what direction you are facing via a pointer, you can practice spinning back to the same direction by just watching your pointer.
In terms of kiting, you'll want to concussive shot and arcane shot, and sting in whatever order. Watch your cool-downs and hit your shot whenever it's available. The exception is stings -- they have a much shorter cool-down their duration, so you don't want to waste mana repeatedly stinging a target once it's already affected.
But kiting is an important skill in PvE. You can kill much higher level melee mobs if you kite effectively. During kiting, you should watch for improved concussive shot. If that procs, your opponent is stunned -- you'll want to get to maximum range, perhaps hit rapid fire, and start unloading multishot and auto shot in addition to your instants.