Level 1-10 - Leinster Edit
Kill trash around Leinster. One circuit should get you from level 1-10 fairly easy just using Light Dart.
Level 11-50 - Devils be GONE! Edit
Go buy a bunch of Greater Invisibility potions and head to the fields east of Kurz (drink up!). You are looking for single Devils. Attack them and summon the strongest Faery you can (Pixie/Farie/Nympy/Queen). You will need to summon several of them and let them attack the Devils. So long as you are invisible they will not touch you. You should be able to GM Thaumaturgy and Mysticism in this time. You can stay here as long as you want, but your next stop will take you from 50-150 fairly quickly.
Level 51-150 - F*****ing Hate Pool Edit
Let's start with the easiest hard fight in this place. Go in the sarcophagus and then go south. You can use the pixie/fairy trick here again if you like, or just cast Mass Hold (Mysticism!). Once you have them locked one way or the other, a couple/few Wrath of God should do the trick and will give you some fairly awesome XP.
Mass Hold will only work on the Thieves and the Bats in this place. Pretty much everything else resists it. Using the Fairy trick, though, you can handle every fight in here except for the Lich, Furies, and Troll Kings. That's alright, though, since you don't really have to fight any of them. Follow this path and kill everything along it for maximum exposure (Locations with a * mean there's a fight).
Sarcophagus - South* - North - Sarcophagus - Lever - North* - East* - North - Door - South* - Lever - East - East* - West - L Door* - South - South* - South - North - North - North - Door - W Door - North* - East - West - South - Door - West - North - Second lever from the right - South - South - West - South* - West* - North* - South - Lever - Third Lever from the Left - Loot - Teleport back to Wen
Level 150-250+ - The Same Fight... Over and over again. Edit
Before I start this guide, I want to remind you that if you are not shifted during this combat, you're about to die.
It's time for the Wasps! Head to the Greater Hives in Ascetos Desert and go to the first fight with five wasps. Before the fight, cast Arctic Grasp and Fire Grasp on each of the Wasps (this is crucial). Once you're ready, Greater Invis and Invuln yourself and then Defenselessness the biggest wasp of the group.
First round of Combat, cast Shift on yourself. Second round fo Combat, cast Mass Berserk, if you get less than 3 of them, cast it again. After that cast Mass Drain on them until all but one has shrugged off the berserked state. At that point, cast pixies on opposing sides of the screen (this is also a great time to refresh your shift!). Once at least four of the wasps are no longer Myst resistant, throw out another Mass Berserk on them and let them finish each other off. Keep up with the Mass Drain until there is just one left. Depending on how many HP he has, you can use the Fairy Queen trick or you can just keep draining him until he's dead (player's choice).
At this point, they should all be dead and you should have a butt-ton of xp (my first time there at 170 I earned three levels). You also want to pick up their maces as they will replenish your mana as you go. Leave the dungeon, go back in, rinse and repeat.
After this, I have no clue where to go or how to run those fights, but you should be able to find a group that will let you tag along, I usually get ones going deeper into the hive. You can give it a try if you like but it's a lesson in futility as the next fight has a Wasp Healer, whom you will quickly learn is a total piece of $#!+, but you can find out why on your own... bring a LOT of mana.