This is a page that gives suggestions on how to level. There should be several different ways depending on the level, gear, and class of your heroes. Whether you need to level an entire low level team, or have 3 maxed character leeching a forth, this page should give you what you need.
Farming bosses is really easy, the concept is to fight the boss as fast as possible. The best formation for low-levels may be composed of anything with a cleric. Just make sure you are atleast withing 5 levels of the boss [plus/minus]. Bosses are farmed because they have a constant XP rate and once you get the hang of their patterns you could easily level up from 1 - 15+.
Most Potent Bosses for farming
[Note: Refer to the Bosses Page for more info and strategy]
1. Samurai Ghost Warrior - Gives a decent amount of exp [1052 XP], also the items drops can help strenthen new heroes for later bosses.
2. Rock Golem - The exp rate may not be as high as it should be. [1260 XP]. But the time needed to clear this boss is like 15-20 Seconds with a good lineup, even if the levels are lacking. Kiting could be a good strat. but if tankable please do so.
3. Ice Golem - High exp rate [3966 XP], and the fact that the Ice Golem is slightly easier to beat than minotaur. This boss is easily kited if you equip high movement speed items, not necessarily stalker rings but if possible do it.
I usually farm Ice Golem to get atleast my new heroes to level 15 before I dare to take them to Chasm. Lastly, if you know more bosses feel free to add more. (≥∇≤)
This is a good way to level a single low level character if you have other strong full level characters to support. Always include a cleric to be able to revive the low level player before the end of the fight.
The arena is a slow process to start with and doesn't pick up for a while. Once you get a lot of accumulated honor, however, the honor you get as well as the xp you get will increase exponentially. After a while, you will get so much xp per fight it can give a full level from 40 to 41. Please note that the arena will only give 1 level at a time unlike other forms of getting xp. (if you are at level 39 with a emply xp bar, and get 2354378673285 xp from a fight, it will leave you at level 40 with a full xp bar. It will take another 1 xp for you to complete the level.)
If you need tons of level 41 characters, the arena will be a good investment to make.