A new player on World of Warcraft needs to understand a few fundamentals of the game in order to have a better experience with the game as they begin to level. To summarize:
1) Bags are crucial to your questing, leveling, and overall comfort while playing. Why constantly have to run back to a town or auction house all session when a few larger bags will help you keep ALL the loot you find.
2) There is no loot that is junk when you start. White gear and basic gray items can be useful when you start leveling, and the meats you pick up are very useful to make money by selling it and the other items to others at the auction house.
3) The bank is your friend. If you are short on time, there is nothing easier than to dump your inventory into your bank in your starting capital.
When you start playing all you have is your backpack and some basic equipment. The equipment will quickly improve but you don’t get a lot of extra bags via quests and you will be hard pressed to loot everything from your kills. You really only have two options: Not loot valuable (copper sale or useful) items. Or run back to town every 20 minutes. The only way to improve this situation is to buy more bags, it is as simple as that.
Starting out , you don’t have a lot of money and you need most of the money to level your skills at your trainer. Pay close attention to how much a wolf pelt or a rabbit’s foot sells for to the vendors, chances are you’ll make a lot more money on certain drops than others. Never neglect your class trainer upgrades in general, but specifically always train at lower levels to get those necessary early dps and healing abilities, they help the grind go so much better. Consider endurance to start, having more energy/mana available and taking on larger groups in combat, rather than quick kills but always having to refuel. This means going Frost for Mage, Protection for Paladin, Discipline for Priest class, etc.
My preferred method to getting bags is to use the auction house (AH). In order to use the auction house successfully you need some money from items made from a trade skill, and the best trade skill early in the game to make money on the auction house has usually been Skinning, Mining and/or Herbalism. If this is your first character chose a complimentary trade skill combination based on your type of armor but if you are looking to make money Skinning and Herbalism is easy money.
You will find the skinning and herbalism trainers in the main towns or capitals for sure, just ask a guard for directions and follow the pointer on the mini map. For Skinning make sure to pick up the skinning knife, For Mining pick up the pickaxe. When you get out into the field, remember that Herbalism and Mining nodes tend to be near monsters so be ready to dish out pain to reap the benefits.
OK, so you have 20-40 copper ore and wish to sell, go to the Auction House and search for your item. Select a price point below the high values but far above the lowest values. Most AH players will be selling the items for very high prices which most people won’t pay. You want cash fast but you want a good return for your items in cash so pick a value that will earn you a few gold over the course of 24 hours. Once you have enough gold you can start buying low and selling high. The more you mine, forage for herbs, or skin determines how much money you can make, along with your investments. You can also announce in the General or Trade chat that you have, say, 20x of light leather to sell for 10 Gold. Just make sure you put it on the Auction House, and state so in your announcement, so that you don’t get swindled by an unscrupulous player.
When you get your money, search for bags on the AH. I have found 12 slot bags are the best bang for the buck in WoW for a while, you can usually pick up 4 12 slots for 10-20g, at least on the servers I’ve played on. Your mileage may vary. Now you can loot to your heart’s content and have plenty of space for those quest items and your Gathering activities.
NB: Picking up a couple 6 slot bags early on can be an alternate route and if you want to pick up a few 6 slots early on just make sure you have money for training. You may have to grind (repetitively kill mobs in the same area) to make your money back but if you want to start Gathering it can jumpstart your money making. The effort you put in determines what you get out of this game.