1-10 | Questing- Cannot start dungeons until level 10 which is where it starts to really pick up
10-50 | Dungeons- would be best if you have a level 90 to run you through these but if you do not just Queue up as a tank or healer for fast queues
10-20 | Deadmines You should hit 20 in about 4-5 runs
20-25 | Stockades About 5 runs, you should get a level or so per run
25-35 | Scarlet Monastery
35-40 | Scholomance Great place to level if your being boosted you can you stay at entrance and get xp
40-50 | Stratholme Just be careful of the Eye of Naxxramas
50-57 | Questing-Blackrock depths then 55-57 Swamp of Sorrows-Blasted Lands
57-80 | Back to dungeons
57-62 | Hellfire ramps or/and Blood Furnace
62-65 | Mana tombs
65-67 | Setthek Halls
67-72 | Utgard Keep
72-77 | Azjol-Nerub
77-80 | Halls of Lightning