When i loot dead bodies, how do i know what im supposed to keep?
Thought I'd expand on this -- check the colour of the item's name.
Grey means it's trash and will rarely be needed. An exception is if you just like the look of the item and want to wear it now and then, like some of the brimmed hats that start dropping around 60+.
White means it'll actually be useful. For gear, it'll have more armour than grey items, but in general the armour rating isn't very important for ranged classes, so you can equip it if you want, or sell it to a vendor. Other materials (mats) will be used for professions, like cloth or meat, and those can also be sold in the Auction House (AH). First Aid and Cooking are two important skills to work on as you level, and much of what you find will be used for them. You'll also use cloth for your Tailoring, and sometimes other mats for certain recipes, like leather.
Green is an uncommon drop, blue is a rare drop, and purple is epic and extremely rare. Most of the time those will be gear that include stats, such as +5 Int. That's the stuff you really want to pay attention to, because if the item will upgrade your stats, you'll want to wear it (mouse over the item and hold Shift to see a comparison between the item and what you're already wearing, and if you hold Ctrl and right-click, you can see what it'll look like). Better stats is a lot more valuable than a better armour rating. And if you can't use the item, you can either sell it in the AH to someone who can, or disenchant it for the mats to use with your Enchanting. As you level up Tailoring, you'll be making a ton of items that you'll disenchant. And over time you'll learn which stats are desired, and which aren't.
...netherweave bags are probably the best size to price ratio. If you're in a guild you can probably find a tailor to make you some, otherwise you can buy them from the auction house for around 10g each depending on your servers economy.
Also, 10-slot bags can be purchased from a vendor for about 2 gold, while 12-slots cost almost 10g. When you check the AH, pay close attention to the number of slots available, because anything with more than 12 slots that's cheaper than 10g will be a bargain. I've often seen 14-slot Journeyman Backpacks going for 5g and less.
One caveat to taking Tailoring and Enchanting now is that you won't have much to sell in the AH. Extra cloth will almost always sell, and it's not difficult to end up with extra enchanting mats so those can be sold too, but you'll have to start watching the prices in the AH for a few days to get an idea about when
to sell, so you can get a much better price. Raw materials sell a lot better than crafted items for most of the game, so sell as much as you can.