Personally, Id suggest staying in Outland until 70, but thats my personal preference. Many people would tell you to head to Northrend as soon as you hit 69.

The two starting zones in Northrend are the Howling Fjord and the Borean Tundra. Pick one, it really doesnt matter which. Again, a personal preference, I happen to think the Borean Tundra has slightly better quest rewards overall. I also happen to prefer the stories there, on both the Horde and the Alliance sides.

Northrend consists of 8 primary questing zones. Of these, it typically takes about 4 to 5 to level from 70 to 80. An average instance run during this will give you somewhere between around a quarter to a half of level, and can given the impression of speeding up the process considerably.

Whichever zone you begin with, I recommend doing the other of the two starting zones second. The starting zones are the lowest level zones in Northrend, and the quests there will turn grey at level 80. This means that should you wish to go back and do them for either gold and/or reputation, you will get less for your efforts. Thus, I recommend getting these two zones completed as a first step. All the other zones in Northrend are higher level, and quests in them will remain at least green difficulty, even at level 80, which means theyll payout a fair amount of gold instead of experience.

Howling Fjord and the Borean Tundra can be connected together fairly easily, even by low level characters. The Tuskarr run a Ferry service from the town called Unpe in BT to Mokai Harbor in Dragonblight. From Mokai Harbor, a second ferry connects to Kamagua in HF. Once youve taken this ferry route once, youll have flight paths connecting across the continent and youll be able to take an air taxi back and forth as necessary.

For your third zone, I recommend doing Dragonblight. Both HF and BT have quests that lead into Dragonblight. Dragonblight contains a considerable amount of the meat of the story of the invasion of Northrend by Alliance and Horde forces. All the quests in the zone lead up to the Wrathgate cinematic, which is followed by the Battle for the Undercity. This set of quests is one of the signature pieces of the expansion, and if you have not yet leveled a character to 80, I recommend it strongly.

Once you reach 74, you will have access to Dalaran. If youve collected the Mokai harbor flight point, youll now be able to fly between your questing zones and Dalaran easily.

If you complete the questing achievements in those three zones, youll most likely be at least level 76. From there you can head into Sholazar Basin, The Grizzly Hills, or (the Empire of) ZulDrak. Having leveled several characters to 80, I like to mix it up and pick a slightly different path each time. Each zone tells a different story and all three are worth learning.

At level 78, I recommend you drop whatever youre doing, and head to K3 in Storm Peaks. There you should collect the quest They Took Our Men! and do that. If youve purchased Cold Weather Flying, youll be able to fly anywhere in Northrend now. If you havent, youll be able to obtain a loaner mount at k3, this loaner is very slow, but will allow you to fly in Icecrown, Storm Peaks, and Sholozar without Cold Weather Flying. The quest I suggested begins the chain to unlock the Sons of Hodir faction. This faction offers special shoulder enchants which you cannot obtain anywhere else. I also typically do all the Goblin quests at K3.

Theres a good chance youll have reached 80 by the time youve finished unlocking the Sons of Hodir faction, but if you havent, fear not, head into Icecrown, and visit your factions flying ship there. On board speak to the Death Knight (Thassarian for the Alliance, Koltira Deathweaver for the Horde). Take the quest Its All Fun and Games. This quest chain unlocks the Knights of the Ebon Blade faction. There are rewards for every class there, but in particular, classes that do physical damage will want the helm enchant they offer.

Youll certainly be 80 by the time you finish that, and in addition, youll be well on your way to achieving important reputation bonuses with various factions.