By participating in The Games, Contractors take a deadly risk in exchange for power, and boy do the Harbingers deliver on their end of the bargain. The climb to the summit of power is precipitous but undeniably quick.
Advancement comes in two main forms: Experience and Gifts and Improvements. Experience is used to improve stats on the Character Sheet, and Gifts are used to purchase new Powers or improve existing ones.
Experience and Gifts/Improvements are awarded only for participating in or running Games.
Other forms of Advancement
Of course there are many other ways to achieve power, and the most effective ways of all are not tracked with numbers on the Character Sheet, but rather with the contents of a Contractor's little black book.
Allies and friendships go a long way. If you can get close enough to a fellow Contractor to call on them after a Game, you have become quite a bit more powerful indeed. This often starts with doctors who make [Downtime] house calls, but it can take many forms. A Doctor has their own problems, and demanding a payment in the form of equipment or a favor for services rendered can quickly turn them into a force to be reckoned with.
Of course, some prefer to eschew friendships in favor of leverage, coercion, and manipulation. . .
A Contractor may also advance by stealing powerful artifacts from other Contractors or coming across such items during a Game. These are not tracked when considering a Contractor's Status, and GMs are under little-to-no obligation to let a Contractor bring all their non-gift advantages on a Game.