Here's how to do it easily (at least for me)
Go directly to the colvert, go northwest into the building in prontera, and agree, you'll be sent to the culverts. make sure you have novice gears before hand.
in the culvert, stay in the first area till level 10 or so, then head down one area. once you reach level 25 hear, go to the third area till level 35. be sure to kill torou's, as they give good exp, are easy to kill, and drop monster feed, which is a nice healing item for a novice early on, and they drop it alot.
once you are level 35, you can either job change into what you want, or go to geffen, go through the tower, and fight poison spores till 40-45 if you're going Super novice, or just want a nice headstart into your class.
from here, i'm not positive, but it's generally accepted, if you a mage/acolyte/gunner/archer, you go into glastheim prison and KS mobs till you can handle geographers nicely, which are north of einbroch, and once you are level 70 or so, you can go back to the prison and kill your own mobs now. if you are a melee class, go back to poison spores till you have job level 41 or more, andf job change. once you job change, if you are a swordsman class, go fight some metallings to gain some job levels, and take on toy factory. if you are a thief class, try the cookies in TF1, and work your way to myst cases. matallings are good for any class, so try those too. if you are a taekwon, go south of einbroch, and kill metallings till you can kill porcellos, once yu are job level 50, (i say this because taekwon skills are very usefull) job change if you want, or try to rank yourself. from there, most melee areas apply. if you are a gunner, follow the ranged portion of my post. as for the ninja, i'm not sure, but i have a nija, and i don't remember where i level'd it. just be sure to get cicada skin shedding, you can take on many more tough opponants then you should be able to with it. i'd say go with sranged weapons till higher levels, then go magic for leveling, but thats just my thoughts.
once you are around level 70-80 as a melee class, sage, or taekwon, try high orcs, they give good exp.