Instructions
Invest in LOTS of food and drink. You'll need it.
Head to Stranglethorn Vale and start killing Venture Co. goblins around Lake Nezferiti. Kill these little guys from levels 34-37.
Travel to Desolace and kill Naga on the islands and shores from 35-38. Watch out for the giants, if one sees you, be prepared to find your corpse.
Head back to Strangelthorn and kill anything along the coastal areas near Booty Bay (Naga, Bloodsails, whatever you find) from 36-39.
Hit the southern Badlands and hunt Rock Elementals from 37-47. There are lots of them, they respawn quickly and they have decent drops from time to time. The Badlands is also one of the best places to farm Mithril and Iron ore. Gold and silver veins spawn here from time to time as well.
Head into the canyon in the western Badlands and farm Dragon whelps from 40-43. Avoid the elites in the clearing and keep your eyes open for more mithril. Truesilver deposits spawn here occasionally.
Travel to Tanaris and hunt Wastewander bandits from 40 to 46. These folks are plentiful and give good drops. They are also the subject of a couple quests, so go after them!
Attack the Naga at the other end of Feathermoon, in Feralas from 44-48. They are fairly tough and can be trouble in groups, but give great xp.
Return to Tanaris and raid the Dunemaul Ogre compound from 45-50. They almost always patrol singly and almost never come to each other's aid. Raid their cave for some extra loot.
Attack the Deadwood village in Felwood from 48-51. Killing these guys will not only help you gain reputation with the Timbermaw Hold (which you WANT), they give good drops.
Make your way into Winterspring and kill the Highborn ghosts that haunt lake Kel'Theril from 49-53. There is a quest to do there, so pick that up in Everlook. The ghosts go down easily and drop lots of good loot. This is especially easy for Paladins.
Travel to the Western Plaguelands and grind the Sorrow Hill graveyard from 50 on. At this point, the skeletons and ghouls will always give you xp (quite good xp until about 56), plus you can gain reputation with the Argent Dawn by killing them (until you hit Honored). They also drop Bone Fragments, which can be exchanged for Insignia of the Crusade at Light's Hope Chapel in the Eastern Plaguelands.