I level every alt this way, and it's FAR from the fastests. I am alliance.
1. Do intro quests in Dark Portal area. Then do the 4 Bonus objectives in Shadowmoon Valley + possibly a few more quests. With 20% potion + full heirlooms, this should put you at level 92.
2. Go to Gorgrond (lvl 92 needed) and do the intro quests to unlock Outpost quests. This also unlocks more Bonus zones.
3. Do ALL the bonus objectives in Gorgrond BUT DO NOT FINISH THEM! Leave ONE mob alive per Bonus Objective.
It will look like "19/20 Slayed" etc.
4. Pop a 300% XP Flask, Rapid Minds and the 20% garrison potion, then travel between each Bonus Objective and kill the last mob in each area. This should make you about level 97.
5. Now, since you are level 95+, you have unlocked all Bonus Objectives in Talador and Spires of Arak. Do as step 3, do ALL Bonus Objectives in Talador and Spires of Arak, DO NOT FINISH THEM, once again, leave one mob alive.
6. Pop another XP flask (Rapid Minds, 300% exp) and a 20% exp potion (if needed). Finish all the Talador and Spires of Arak Bonus Objectives, meaning you kill the last mob. You have plenty of time.
7. You are level 100, this takes like an hour and requires 2x 300% and usually 1x 20% exp pot.
And there are faster ways, I just prefer this, as it's solo.