Classes
Use the following setup to level yourself the quickest
Berneli + Scout + Fighter

I completly understand that you can't even get Berneli until about level 30, till then use a stock musk.

Berneli so you can rock out her shot gun to help powerlevel your future characters

Scout so you don't die while AFKlvling

Figther because they are the most diverse character (bar Catherine who can use every stance basically) by leveling up your fighter you will be able to use them for just about every task PVP, PVE, Raid, etc... Besides, Berneli doesn't have the best health (thought her armor can be slightly improved over that of a stock musk) and a character with a little bit of tank ability helps out greatly


Location
Find a place that looks like this (lines = wall, periods = space)
.....|
.....|
.....|-------
..............|
..............|
Mob......|

Arange the character as follows
.....|
.....|
.....|-------
............s|
..........b..|
........f.....|


Scout set with Medic/Bard
Berneli set with Shotgunblaster
Fighter set with Blandir Cruz (Polearm) or Short Guard (Raiper)

The stances are chosen for their ability to do AoE with standard attacks
Berneli's stance allows it to hit 3 targets per shot if they are close enough (not 100% confirmed)
Polearms hit about 4 to 5 per attack (not 100% confirmed)
Short Gaurd hits 2 per attack (confirmed)


With this setup you can afk level yourself to 60 in about a week without trying. In order to powerlevel after you get berneli up to about 90 use the following setup.
X represents the character to powerlevel
*Notice Berneli is further west, this is so she can pull a little more of the mob
.....|
.....|
.....|-------
..........sX|
........b....|
..............|