Skin every beast that you kill. It takes a few seconds, and gives you items to use for Leatherworking or sell.
You must completely loot a body before you can skin it.
If you have autoloot on you also will autoloot your leather making it a lot faster and less tedious
Make sure you have capacity in your bags. The various forms of leather, scraps, cured hides and fel hide stacks in stacks of 20, unaltered hides in stacks of 10.
Remember the rule for skinning mobs killed by others, that it is generally best to wait for people to leave so that you avoid ninja skinning.
Don't be afraid to follow a non-skinner who is killing mobs and skin their kills. People normally don't mind, and it's free leather.
Go to areas where people are killing lots of beasts, and skin corpses that other people have killed and left. This is an easy way to level up your skinning quickly. Good areas for this are spots just outside towns/cities where people are killing a certain number of a beast for a quest. But please don't skin a corpse until the killer has moved away — he may be a skinner himself, and skinning a corpse before he can ("ninjaskinning") is considered very impolite. Rhino meat farmers in Borean Tundra are a good source.
The chance of gaining a skill point in skinning depends upon the color of the word "Skinnable" in the tooltip for the animal. The levels are:
Grey: No chance.
Green: Light chance of skill gain.
Yellow: Good chance of skill gain.
Orange: 100% chance of skill gain. NOTE: at higher skinning levels "orange skinnables" will not always give a skill gain after every skin.
Red: Can't skin.
Finkle's Skinner or the Zulian Slicer, and the +5 skinning enchant on gloves can take your skill up to 465, and if you are wearing both weapons skill is maxed to 475, wich is more than enough to skin everything in world. When next expansion comes out, the +25 skinning skill boost will always be handy.
If leveling skinning, seeking large groups of mobs will speed up the process. For Example, in borean tundra there are tons of rhinos. You will get lots of Rhino meat with little extra effort too.