I'm not very far into Disgaea yet. I've only made it to Map 1-4: Hall of Caresses, and the mid-boss keeps beating me there. I figured it's because I just bought my first new characters (3 of them, a healer, a red skull, and a brawler) and they're all only level 1. They keep getting one-shotted and die. The ranged enemies seem to specifically seek them out.
My thought was that I should go back to the previous map, Map 1-3: Corridor of Love and try leveling them up there. This walkthrough seems to support the idea that it's a good spot to level characters up to level 5.
However, the problem I'm having is that I don't fully understand how experience gain works. It appears that I only get experience by doing damage, or maybe even just for killing blows. So my plan of bringing my level 1 newbies onto the map while my level 5s ran around and killed everything ended up not working, as none of the newbies leveled. I had the level 1 healer following them around and healing, but the act of healing also doesn't seem to grant experience (or if it does, very little, as she's still level 1 too after burning off all her spell points on heals). So I tried the map again, this time attempting to get the newbies into the fight, but just like in the Hall of Caresses, they keep getting one-shotted and die.
This seems like a problem that's only going to get worse as I get further into the game. I'm hoping I have more options than just sticking them on the easiest map possible and building my way up from there. That seems like it will drive me nuts if I keep having to play the tutorial maps whenever I create a new character, and I'm hoping there are better options.
What exactly governs when characters earn experience points, and what's a good strategy for leveling up new characters?