EXP Bonuses: Every now and then, there will be bonuses to the exp from killing a mob. So, for some period of time (usually 3-6 hours?), everyone gets a bonus to exp while ranking (up to double exp). Also, you always get a bonus to EXP when there are fewer people online (to 40% I think). The 'bonus' command will tell you if there's a scheduled bonus coming up.

Merc as groupmate: Only city bought mercs give the bonus. When you 'gr' they will have an * by their name to verify the exp bonus.

Of course, if you want minimal ranking time, you can roll a neutral bard or a defense/offense or defense/utility shifter.