Zones are numbered by the level range they're meant for, so just follow the numbers up as you level. Kalimdor and the Eastern Kingdoms cover levels 1-60, and once you hit 58 you can catch a boat or zeppelin to Northrend and continue from there up to level 80. Contested zones have quest hubs and camps for both factions, so watch out for enemy players on a PvP realm.

While you level, keep an eye out for World Giants and the Gate Event — both scale their rewards to your current level, so you'll gear up naturally as you move through these zones.