The Execution Room, which is new to Zenonia 3, is a very easy way to level your character early in the game. Once you get to the town of Delfoy do the little side missions and a few of the main ones until you get level 10 or higher. This wont take long if you are adamant. Once you can at least clear one room you get about 2800 XP for this which is a massive amount for a low level character, you also get very nice (albeit random) equipment that is usually magic or above classed. The equipment that you get is a level or so above you which will give you something to work towards. You will die a lot, but don't use any origins of life unless you have lots of them or a lot of Zen on hand. There is no penalty for death in the Execution Room, you just get sent to the very first room and you have to clear it all over again. The monsters and mini boss legendaries that you fight will be randomized each time you enter a room, so don't expect a "watering" creature on the first floor every single time. You are gonna have to grind it for a while to fully exploit the room, but each room cleared stacks XP and that gets to be a pretty large amount for just a few rooms cleared which can get you a level or two in just a few minutes if you play your cards right and heal when necessary.
Note: You get a little bit of HP and SP back when you enter a new room, and when you die you get it all back.