- Accomplish something unusual. This could be a lot of things, and I plan on making an easy-to-use index at the back, so when you do something weird you can look over the Advanced Classes thing and see where that fits in.
- Join an Order. Orders are always looking for Heroes (after the Greek tradition, don't worry- no knights in shining armor connotations here. That's why I make sure to capitalize it, actually), and you can probably join. Orders are the big movers and shakers of the world and are ideal for adventurers because they're generally not interested in the status quo the same way kingdoms and baronies are, and they're generally pretty lenient as far as dues/attendance goes.
- Train under a Mentor and gain an advanced class,depending on what you've done.
- Do something else extraordinary, and get further advanced classes as you level.
One of my biggest personal pet peeves is where 'adventurers' fit into a campaign world, and exactly how scuzzy that adventurers really are. I mean, you give these guys a bunch of hit dice and armor and stuff, and then thrust them into a campaign world full of kings and dragons and stuff and either a) expect them to go find something, or b) straight up tell them what to do.
I know, I know, that sounds like a campaign world problem, but hear me out. The problem is that during character creation, you're relying on the whimsical ethers of the players' minds to decide what sort of organizations are out there, and that can be rough when the players don't know what to pick. Orders give a little bit of structure to it, and are kind of like a GM Guarantee that not only is that archetype totally permitted and you should go for it.
Of course, it's important to leave the option in there for people who really don't want to have that connection, because that's a valid place in the world, too.