Few people realize that you can stop doing quests and grind your way to max level. I recommend doing this no earlier than level 10. Below I’ll explain how you can avoid the monotony of doing quests (and replace it with the monotony of killing the same few things over and over) from level 40 to level 50.
Grinding in Eastern Plaguelands (39-45)
Our first stop is in Eastern Plaguelands. If you’re following this guide sequentially you’ll already be in the adjacent Western Plaguelands. Start by heading to Light Hope’s Chapel. In the surrounding area, called the Pestilent Scar, you’ll find bats, hounds, gargolyes and grubs. Slaughter these until level 42.
At level 42 you can head south and east and into Tyr’s Hand. Back in the day, this used to be a level 60 area full of elite mobs. I would go in there and struggle to solo the elites to farm Runecloth. Back then it was epic, now you can just run through and slaughter the Scarlet Crusader collecting less valuable Runecloth.
Grinding in Badlands (45-47)
Once you reach level 45 we will launch an assault against the Dustbelch Ogres. There are four camps of them, Cagg, Kosh, Boff and Wurg. Slaughter these guys mercilessly along with nearby beasts until you reach level 47. Afterwards, we’ll head west to Searing Gorge.
Searing Gorge (47-51)
In Searing Gorge you’ll find the Grimesilt Dig Site on the eastern edge of the zone. Here you’ll find golems, dwarves and some spiders around the edges. You can stay here until you reach level 47 or 48. After that, head to the east to Iron Summit where you’ll find more dwarves, spiders and elementals. Stay here until you reach level 51. You might find it necessary to start on the east side and work your way west as you get higher level.
Tip: Have you ever wondered how players have so many level 85s or how they can level an 85 so quickly? I use and strongy recommend Zygor's in-game leveling addon which will enable you to level in 5 days of played time. You can find a free version of it here.