Leveling
Leveling Suggestions - in ORDER

Starting Zone
Second Zone

Should be level 10 now

Northern Barrens
Azshara
Ashenvale
Northern Stranglethorn Vale
Southern Stranglethorn Vale

Should be level 35 now

Western Plaguelands
Eastern Plaguelands

Should be level 45 now

Badlands / Searning Gorge to 51
Swamp of Sorrows to 55
Felwood / Winterspring to 58
Blasted Lands to 60

Burning Crusade content 60-70
Lich King content 70-80
Cataclysm content 80-85
MoP content 85- 90