The baseline of this post is for those new to TBC. Based from my experiences. I will details some important quest that you guys should follow, note that I haven't done all the quests in Shadowmoon Valley and the Netherstorm yet. I will not mention Dungeon questslines in here.
First map you would be is in
******Hellfire peninsula (Recommended level 58-63)********
Instance: Hellfire Citadel
Here is where you will first set foot on the outland. The map here involves a lot of kill monster count with same average amount of get items from monster count. This map is involved 1/2 group 1/2 solo quests.
There is a quest that involves a trinket here that you could use in conjuction with another trinket. However the questline isn't that long, about 8 steps and its fun. completely soloable except the last boss
The trinket is extremely good and the equivalent of black hand breadth/eye of the beast with an on use effect.
Upgrade level : Great
Chest Armor questline
Another quest here that involves a blue chest armor which could replace t1
This map is a pure solo/ pick up items quests; with a small share of elite quest involved.
Notable Quests: To be updated
Can't remember any good quest in here, besides the typical farm reputation.
********Terokkar Forest (62-65)***********
This map is where you'll find Shattrath City; and will probably become your most hated/favorite place in the game. You'll be surprised when you see familiar opposite faction players spitting on you and you can't attack them, but neither can they lol
Terokkar Forest start off with 2 homes, for your faction and for SC (Shattrath City) and at the same type it is a major turn since in one of the entrance quest to Shattrath city involves you to choose between the Aldor faction and the Scryer faction. I recommend you to search the rewards for the exalted level of these two factions before you make your choice.
Notable Quests: TO BE UPDATED
Big boner questline: This questline starts off with escorting some dwarves and ends up with you and at least 2 party members on fighting a big worm, however you should keep in mind that the reward on this quest are only 3 daggers.
UPGRADE LEVEL: Medium
This is where the kick comes in, this map involves many group quest from 2 people group quest to a full group quest, most of the final quests here are elite, for some classes it is easy to solo, but most of them its is not possible.
Ring of Blood Questline: This is a questline that ends up with a great weapon the minimal requirement is of level 65 however you might need a full party for this, and make sure EVERYONE on the team is on the same step to avoid repeated kills. The NPC to start up the quest are on the northwest corner of the map http://www.wowhead.com/?npc=18471
UPGRADE LEVEL: High
Hero of the Mag'har Questline: This questline...you could call it tedious but the reward is worth it; along with reputations that you can get for the maghar faction. However this questline DOES NOT starts unless you have completed the blademaster's chain and altrius' chain.
So as soon as you get to Nagrand start up with all the kill ogre quests; you'll eventually end up in this chain.
UPGRADE LEVEL: High
****************Blade edge's mountain**************
An average map, similar to hellfire peninsula. You find a small share of elite quests (actually there are only 2 or 3) and a large amount of solo quest.
Death's door Questline: