This is yet another guide that I have found online and it has a great foundation for WOW power leveling effectively, so I decided to add it here for your enjoyment! Why add another WOW powerleveling basics guide? Great question, I added it here because I feel that if you don't have the powerleveling basics down you will not WOW power level at the speed you really can achieve. Just like learning anything you must MASTER the fundamentals to really become a master. Just think of this as a beginning mastery course for World of Warcraft powerleveling!

1) Take as many quests as possible and at the same time, try not to do quests one at a time. When entering a new area, find all the quests from NPC's first, before you start killing things.
2) A complementary group of 2 or 3 (such as tank + healer) is sometimes far better than solo'ing. Especially when a quest calls for "kill X amount of something". Use groups when they suit you. Leave a group when it bogs you down.
3) Play a Multi-Zone game. When you hit WOW leveling 10 or so, it's time to run to the nearest "other" starting area and do the quests there. You will do them fast, and get exp for all the kills (as long as they are colored green to you) Doing a load of quests 3-5 levels beneath you really racks up EXP fast.
4) Green quests are your friends! These are quests that are 2-3 levels beneath you. When I get a bunch of yellow colored quests, sometimes I'll just 'level grind' 2-3 levels, then power through the quests solo. It basically comes to this: If you are getting killed more than once doing a single quest, you are wasting time- it's better to grind a level and do it later.
5) Dont be afraid to dump quests It's so tempting....you just don't want to let go of that quest that's been in your books for several days. It requires you to run around the world - see this person, see that person...will take you 3 hours. Or that quest you forgot to do way back in Elwynn Forest, and now you're all the way in the Wetlands. DUMP IT. There are thousands of quests in this game. Wasting 4 hours just to 'finish' that green or gray quest is not worth it. Abandon that quest, and replace it with others.
6) WOW power Level Grinding still works! This is killing monsters that are GREEN to you. Why Green? Because you kill them fast and with very little down time. You can basically steamroll through dozens of con-green enemies in minutes! Spend an hour or two doing this (boring ya) and you'll see what a difference in EXP it makes! Small EXP gains over a long period time really add up.
7) Decide if you are going for power or wealth (or both) before you decide on your profession. Ask yourself, "will mastering this profession take too much extra time and hinder my primary goal?". Take professions that do not hinder you.

After playing World of Warcraft since beta, and logging in hundreds of hours over numerous characters ever since, I can tell you from my experience that the fastest way to WOW power-level up and make cash is to take as many quests as possible, and follow some basic principles.