CleverNickName,
here's what my 'sandbox' looks like.
I want the game to feel like the cape-and-sword novels by Dumas, Sabatini, Orzcy, Weyman, and Pérez-Reverte, so one of my early planning steps was to identify
some of the shared elements of swashbuckling tales - the adventurers are involved with historical figures and present for historical events, social conflict is as important as martial conflict, coincidences are common, and so on - and figure out ways to incorporate them into the game.
Accordingly I filled up my setting with lots of historical figures as non-player characters and projected a timeline of future events based on the history of the period in which the adventurers may become involved (frex, a soldier called to campaign in Italy or join the siege at La Rochelle) as well as some fictional events connected to historical occurances (frex, intrigues surrounding the marriage of Louis XIII's sister to the Prince of Wales).
Coincidences present a bit of a challenge in a
status quo, 'sandboxy' setting - if the adventurers are free to go where they please and do what they will, how do I introduce coincidences without plopping down encounters in front of the adventurers? The answer for me was random encounters. I consider random encounters to represent the 'living' setting; they are also a means of subtly reinforcing the genre, so for my random encounters, I created situations involving different npcs from the game, most of whom are connected to one another in a complex web of relationships.
Frex, the same knight of Malta appears in two different random encounters - a duel upon which the adventurers stumble and a visit to the horse market of Paris - and he is connected to the participants of two others, so should the adventurers meet this particular knight of Malta as a result of a random encounter or some action they've initiated during the course of the game, there exists the possibility of a (literal) 'chance encounter' with the chevalier or his friends somewhere down the line. In this way I'm able to include the genre element of coincidences while preserving the sense of a living setting and a light touch on my part as referee. I've no idea when or even if the chevalier will become involved in the campaign, and if he does, I have no idea if he will end up as a friend or foe of the adventurers - that will depend on them and how they deal with the situations in which he is presented.
I also deliberated about what ruleset I wanted to use. I ultimately opted for
Flashing Blades for a number of reasons: a great combat system that captures the feel of [ame=http://www.amazon.com/Fight-Direction-Stage-Screen-William/dp/0435086804]William Hobbs' fight choreography[/ame], genre-appropriate player characters, and career rules which give the adventurers the chance to grasp the levers of power and influence over time and change the course of history in actual play.
One of the rules which add to the genre-appropriateness of the adventurers is Advantages and Secrets. Like many of the characters of cape-and-sword tales, the adventurers may choose an ally, or a title, or a secret loyalty, and so on - consider d'Artagnan and M. de Tréville, Berault and Cardinal Richelieu, Alatriste and don Francisco de Quevedo, and so on. Advantages and Secrets can provide an adventurer with a resource to call upon during the course of the game; unlike many referees, however, I don't use these as sources of 'plot hooks' because I have no plots
per se on which to snag the adventurers - it's up to the player to decide how to best utilize an Advantage like Contact or a Secret like Secret Loyalty in the course of playing the game.
(Note that this is one of the areas where
pemerton's approach and mine differ - if I've understood correctly, the adventurers in
pemerton's games begin with a broader range of connections to the setting and the characters therein on which they build, whereas I prefer that the adventurers begin with only a strand of a connection then develop more in actual play. After many posts back and forth, I've come to the conclusion that we are chasing similar experiences in the games we run, but
pemerton directs his efforts from behind the screen at the inner life of the adventurers while I prefer to manage their external circumstances. Two different approaches with similar goals - and isn't it great that our little hobby makes both of them possible?)
So, like you,
CleverNickName, books and movies do influence how I approach my game, but they do it in terms of genre-emulation rather than story structure. I prefer to put as much of the focus as possible on actual play, and to make the adventurers real protagonists in that they drive the game by their choices; my job is to have the setting react accordingly. In my experience this produces rising-and-falling action as the adventurers lay their plans and attempt to execute them.