Novice to First Job
As a Novice, you may start by fighting Porings, Lunatics, Drops, and Pupas at prtfld_08 which is the lower map from Prontera. If you are choosing archer as your first job, start your journey at Payon and hunt for Willows as early as level 1. This will make your job change to Archer easier. If you are choosing a Merchant as your first character, pick up loots to sell to the NPC as part of your quest demands for a payment of 1,000 zeny.
After your job change, you may choose to grind your levels, use the Eden board quests, or complete the different Monster Quests. If there are people playing with you, it is better to form a party to level to take advantage of the +10% exp bonus per party member.
A common leveling area is hunting Wolves 2 maps down from Payon. With your Mercenary, you can kill Wolves with ease. Beware that attacking a Wolf will aggro Wolves in the vicinity so plan your attacks well.
You may also go to the ever trusty Payon cave one map above Payon.
After gaining a couple of levels, Archers and Mages may opt to hunt Geographers. They are unmoving plant monsters that give a lot of exp. To reach the Geographer map, you can just easily warp via Iris Employee then choose Einbroch Field 4 which only costs 5,000 z. Remember, beware of going near Geographers, they do a lot of damage. They also heal each other when in clusters.
For Thieves, they can try their luck with Toy Factory 1f and hit Cookies and Mystcase. As there are almost no aggressive monsters here, you can take your time in killing mobs. Loots from here sell for a lot in NPCs so it is also profitable. Watch out for the Chepet, Mastering, and Angeling monsters though as they are aggressive.
After gaining a couple of levels (usually when you reach level 51 and you aren't able to use a mercenary anymore), you may move to the following maps:
- Archer/Mage -> ein_fild04 (1 warp above Einbroch)
- Thief -> xmas_dun01/xmas_dun02 (Toy Factory)
- Swordsman/Merchant -> orcdun01 (Orc dungeon)
- Acolyte -> form a party with someone :)
After choosing your 2nd job change, your farming places will increase. But the most common level up place will be the Magma dungeon. Party up with other characters and try your luck going to Magma 2F.
If you are a Hunter playing solo, you may want to continue hunting Geographers until you reach level 80 then you can try your luck with Stings at Glastheim culvert. These mobs drop Gloves  as well as Bow Thimble which are good accessories for you.
If you are a Knight, you may want to try hunting Minorous at Pyramid Basement 1. Spam pierce to quickly kill Minorous. You can loot them for Rough Oridecons, the Two-handed Axe , and for their card. These items sell well to players via #market or vending.
If you are a Crusader, you may want to try Orc Dungeon until you are strong enough for Glastheim's Chivalry. Raydrics and Khalitzburg drop a variety of items sought by players, most importantly the Raydric card. Steer clear of Abysmal Knights until you are strong enough to handle them. Watch out for Alice and try your luck in killing her for her card.
If you are a Priest, you can go solo leveling by killing Anubis at Sphynx 4. Though you can also look out for parties.
If you are a Monk, monks may try using finger offensive and attacking Sleepers at Einbroch fld_08. Not only do they give high exp, but their loots also sell for a high price.
If you are a Wizard, you are one of the most sought after jobs for party leveling at Pungus or in the Magma dungeon. Best capitalize on this. For Sages, although some are able to join Magma parties, they are not the top priority. They may opt to level in Geographers or in Seals at Comodo.
HOWEVER It's still recommended to level with a party. Not only is it cost-efficient but also because you can have in-game friends you can play with. Also, there is a +exp boost for every party member and for a full party.
If you want to go solo, you will need some decent equips to go to these common level sites:
- Hunter -> Sting @ Glastheim Culvert (gl_sew03)
- Assassin -> Anolian (cmd_fild03)
- Sage -> Seal (cmd_fild08)
- Knight -> Minorous (moc_pryd05)
- Crusader -> Raydric, Raydric Archer (gl_knt01)
- Priests -> join a crusader or knight in their leveling :)
- Monk -> Sleeper (ein_fild08)
- Wizard -> Party up in magma!