Choose an easy class to level if it's your first character, such as hunter and paladin.
Carefully decide where you talent points will go. Prioritise:
- Reducing your downtime
- Improve your survivability
- Improve pets damage and survivability (Warlock/Hunter Only)
- Improve your main spells damage
Try a mixture of questing, random instances (through the Dungeon Finder system) and random battlegrounds.