This guide is based on my own personal experience and scouring the 2005 internet for old tips and guides, please feel free to contribute to the guide by posting any helpful information or corrections you might have.
FULL DISCLOSURE: This guide was written for another server a few years ago. I'm currently leveling an I/L on Phoenix and will make adjustments as I go. Appreciate input from those who've already done the grind!
Levels 8-15
Victoria Road: Henesys Hunting Ground I
Blue Snail, Red Snail, Shroom, Slime, Orange Mushroom, Green Mushroom
Stick mostly to the bottom two platforms
Dungeon, Southern Forest I
Slime
Victoria Road: The Tree That Grew II
Slime, Stump
Levels 15-20
Hidden Street: Mushroom Garden
Shroom, Red Snail, Orange Mushroom
Victoria Road: Henesys Hunting Ground II
Blue Snail, Red Snail, Shroom, Slime, Orange Mushroom, Green Mushroom
Victoria Road: The Rain-Forest East of Henesys
Pig, Ribbon Pig
Hidden Street: The Pig Beach
Pig, Ribbon Pig, Iron Hog
Levels 20-25
Dungeon, Southern Forest IV
Green Mushroom, Horny Mushroom
Kerning City Subway: Line 1 <Area 1>
Bubbling
Kerning Party Quest
For levels 21+
Levels 25-30
Dungeon: Ant Tunnel I
Horny Mushroom, Zombie Mushroom
Hidden Street: The Land of Wild Boar II
Wild Boar, Dark Stump, Axe Stump, Dark Axe Stump
Kerning Party Quest
For levels 21+
1 Energy Bolt
5 Improved MP Recovery
Max Improved MaxMP Increase
Max Magic Claw
Max Improved MP Recovery
Max Magic Guard
After putting 10 points into Magic Claw, save the rest until you have enough to max it. Level 11 Magic Claw drastically increases MP usage for minimal damage increase.
Levels 30-35
Kerning Party Quest
Level 30 only
Dungeon: Ant Tunnel I
Horny Mushroom, Zombie Mushroom
Warning Street: The Burnt Land I-III
Fire Boar
Ludibrium: Terrace Hall
Brown Teddy
Ludibrium: Sky Terrace <2>
Brown Teddy, Pink Teddy
Levels 35-40
Warning Street: The Burnt Land I-III
Fire Boar
Orbis: Garden of Red / Green / Yellow I
Jr. Cellion / Grupin / Lioner
Ludibrium: Sky Terrace <2>
Brown Teddy, Pink Teddy
Ludibrium Party Quest
For levels 35-50
Levels 40-50
Hidden Street: Lorang Lorang Lorang
Lorang
Weak against lightning
Victoria Road: Tree Dungeon, Forest Up North III
Curse Eye, Fierry
Dungeon: Cave of Evil Eye IV
Evil Eye, Jr. Boogie
Kerning City Subway: Line 1 <Area 4>
Wraith
Orbis: Garden of Red / Yellow I
Jr. Cellion / Jr. Lioner
Weak against ice
Ludibrium: Eos Tower 2nd Floor
Ratz
Good for mobbing with lightning bolt
Ludibrium: The Path of Time <1>
Platoon Chronos (Drops GFA 60%)
Ludibrium Party Quest
For levels 35-50
Levels 50-70
Florina Road: Hot Sand or Hidden Street: Clang and Lorang
Clang, Lorang, Tortie
Clang drops Yellow Umbrella (I'm not sure which map is best for Clang, please correct me if this isn't it!)
Orbis: Garden of Yellow/Red II
Cellion, Lioner
Weak against ice
Hidden Street: Dangerous Valley I
Fire Boar, Copper Drake
Hidden Street: Dangerous Valley II
Fire Boar, Copper Drake, Red Drake
Red Drake - weak against ice
El Nath: Forest of Dead Trees I-IV
Coolie Zombie
El Nath: Cold Field I
Hector
1 Teleport
1 MP Eater
Max Thunderbolt
2 MP Eater
Max Meditate
Max Cold Beam
Max MP Eater
Max Teleport
1 Slow
As with Magic Claw, you can hold SP from Thunderbolt once it reaches level 15. Max it once you have saved enough points.
Thunderbolt and Cold Beam can be switched depending on where you prefer training early on.
You can skip Cold Beam altogether if you like and bump everything else up. Spend the extra points on anything you like.
Levels 70+
El Nath: Forest of Dead Trees I-IV
Coolie Zombie
Ludibrium: Forgotten Path of Time <3>
Death Teddy (Recommended at 75+)
Ludibrium: Warped Path of Time <4>
Spirit Viking (Recommended at 85+)
El Nath: The Cave of Trial III
Bain, Jr. Cerebes, Cerebes, Firebomb (Recommended at 90+)
Hidden Street: Twisted Time
Gigantic Spirit Viking (Recommended at 95+)
Max Ice Strike
3 Elemental Amplification
11 Spell Booster
Max Elemental Amplification
Max Spell Booster
Max Magic Composition
11 Seal
Max Partial Resistance
Remaining points into any skill
Realistically, this is your last job anyway - so once you hit 70 you can just add the rest of the points you gain into anything you like.