Well, there are lots of quests out in lovely Despair. Some are very nice in XP rewards. Once you find these, and as you go forward with your first fighter (recommended to gain good gear and explore) you'll start to notice a pattern or two. The first is that there are certain quests you can do over and over, and certain ones that are only once. Learn which gives what, and when you have acquired enough gear for your dream toon, and you are ready to start playing that one, do those high XP quests AFTER you go legendary, so their XP will carry more weight, so that reward will go further, as you cannot use the XP Bank once you go legendary.
Remember that going legendary carries with it a certain level of finality. You take an XP hit upon going legendary, so read the signs and talk to NPCs that offer information on going legendary.
There are other times that toons will not be able to use the XP Bank. Some of these are RDD characters, as leveling up and re-leveling is an exploit that is checked for, and certain subraces are restricted (bonus ones, for example) to make it harder, more challenging and to earn your bonus levels fully.
I hope this helps.