Well, I'd advise you to do all quests regarding addmiting to guild, regardless of which guild you chose. You do them all, just about BEFORE you definatelly chose to apply to a guild. They all give you nice XP. For example, when you're about to join, say, Old Camp, go to New Camp and to the same there, same for Sect Camp.
There's a cook in Old Camp, looking for Hell Mushrooms to make a "soup"

I can't recall exactly, he also gives you XP; you could try fiht in arena as well, but those guys will bust your head in a matter of few... there aren't that much side quests, but if you look carefully you will find them.
See the quest with Rice Lord in New Camp.
Best regards, samurai.
