-Hire an NPC and just kill him or her. This works well if you hire Otis, Elmo, Lareth, or any high level character.
-After earning an Elemental Gem (easiest with Earth, Air, and Water), use it to summon a demon. Use a Rogue or Fighter to melee the demon with full attacks and kill it before the duration expires. Once it dies, loot it to retrieve a free Elemental Gem for another character, at no risk, plus gain the experience for killing the creature.
-When first starting the game, create your primary character and two or three others that you will import later. Start the game using only your primary character. Walk around Hommlet and talk to everyone so that you initiate as many of the side quests as possible. You will be able to finish some of them very quickly. Complete as many of the non-combat quests as possible, and since you only are using one created character, you will level him/her up many levels quickly. If you want to complete the three romance quests, you will need two male characters and one female character. Note: The two romances with the female NPCs may not activate if you are using evil characters. Go to the inn and import two characters of your choice. Make sure one is some type of offensive mage. The other can be whatever class desired, but if you choose another spell-caster make sure you hire Elmo, as he is a great high level fighter. Go out and complete the combat quests, but make sure you protect your new characters. Elmo can take care of himself. In Emrity Meadows, avoid the Bear and Giant. They are high level and the Giant can kill your party members with one blow from his club. Return there later after you are at higher levels to kill them. After leveling up to about level 5 or 6, go to the Hommlet Trading Post and kill Gregmag and Rannos. They give you a large amount of experience points, and since they are evil, you will not receive a reputation penalty. With your primary character now at a high level and Elmo along, you can easily defeat most enemies while you protect and level up your spell-casters. Also, in Nulb you can kill Otis for some good experience points and equipment. Otis is Elmo's brother, and if you choose to fight Otis, Elmo will side with his brother. This is a difficult fight at lower levels, and Elmo is more valuable as your ally if you are only using three or four of your created characters. If you want to defeat Otis, turn Elmo loose first. After you kill Otis, you can return to Hommlet and Elmo will rejoin your party.
-This trick requires a Cloak Of Elvenkind and a Dexterity of 18. Go to a place like the moathouse and look for a very tight corner. It can be on the inside or outside the building. While in the corner, open the radial menu and turn "Sneak" on. Once this is done, rest for a period of two to five days, as many times as needed. If performed correctly a group of ten to thirty monsters will be located near you, and a couple on top of you. Kill them for experience totaling from 1,000 to 3,000 points. This works best with two characters. One wizard and one fighter with Greater Cleave works very well. Remember to have them both in hiding, and use the fighter as the bait. You must be facing away from the monsters for it to work, the wizard needs to be a distance away. A Fireball spell makes this trick work extremely fast.