Some aspects of pacing are pretty clear. I think most DMs understand (and players prefer) that campaigns start with something interesting to make the characters care about the story, like a surprise fight that unites the party or a mystery that requires their attention. Most campaigns also end with a difficult fight against a powerful, narratively significant enemy. Even if they’ve never heard this terminology, players can agree that campaigns tend to start on a mild crest and end on a very high crest.
The short-term pacing for an individual session or fight is harder. It’s like the pacing for an episode of a TV show, opposed to the pacing of a season or a series. It’s the rise and fall of a particular scene in a movie or boss fight in a video game. In general, players are going to end a session or fight in roughly the same place as they started it because only so much can occur in a short time. But it’s still important to look at the excitement level even in the microcosm of a few hours of play.
Most DMs I know like to either start a session on a crest or end on one. If you start the session with something exciting, you can get players interested right away and, if the crest is a combat or something else with an unambiguous beginning, make it clear when the pre-session discussion stops and the session proper starts. If you end the session with something exciting, you can build to it over the course of the session and keep players progressively more interested. You can get the best of both worlds by ending a session on a cliffhanger that gets resolved at the beginning of the next session, but it doesn’t always work with the flow of the story. If it takes two hours to build to a cliffhanger and two hours to resolve it, then the whole campaign is built around a sine wave of pacing, which is just as predictable as a flat crest or trough. Generally, the most effective pacing changes are unexpected, but I’ll talk about that more in a later post.
As I said last time, it’s easy to think of a fight as a crest, and often that’s true. It’s the situation where the characters are in the most obvious danger, where choices needs to be made quickly and have the most direct effect on their health. To be fair, not all fights are crests; some are fairly mundane and easy, the D&D equivalent of a squash match (or, for the more adult readers, a curb stomp battle). But most are, and in this case the post-fight rest is a good trough.
Using fights as a crest usually works, but it becomes a lot harder depending on what you’re running. Imagine a D&D session that’s five hours long, which is plenty of time for a session. If every fight is fifteen minutes, you can fit twenty fights into that session (though you’re likely spending time on story, exploration, interaction, party maintenance, and faffing about, so don’t expect more than five fights tops). But if every fight takes two hours, you can only fit two. Fights get longer at higher levels in every edition of D&D, and at any level 4th Edition combats take longer than 3rd Edition. When you consider adding a fight to a session, you have to consider how much of the session it’s going to consume.
Long fights aren’t a death sentence for pacing, though. A good long fight tends to go through its own short crests and troughs, some of which are planned (new monsters arrive, an enemy uses a powerful spell, the terrain changes) and some not (somebody gets a critical hit that kills a powerful enemy, one side or the other goes on a string of missed attacks). One of the explicit goals of 4th Edition is to improve the pacing of combat, giving players encounter powers so they can do neat things in every fight and don’t resort to “five-foot step, full attack” every round (this is one of the reasons we refer to Essentials as “edition 4-point-minus-3”, because some of the classes took away the changes that even I, with my disapproval of 4E, saw as improvements over 3E). This is also why players and monsters get scarier when they’re bloodied. It shifts the balance of power, which puts the results of the fight into question, which increases excitement and interest.
There are also non-fight crests. When players meet a new or important person, or when a trap comes out of nowhere, or when a big mystery is presented or resolved, these are all crests. A lot of these have to be balanced against the longer-term excitement level of the campaign (the players can only meet the king for the first time once) so it’s harder to throw them on short notice into a session that’s lagging. As a general rule, I like to keep a couple of sub-plots in my back pocket that fit into the campaign but aren’t wholly required. If things get bored (or, more likely, if the players are doing too well), I’ll toss in an extra complication; it’s usually either one that needs to be resolved quickly, so that it doesn’t really affect later session, or one that can be safely ignored at the possible expense of some later complication, which gives me time to figure out how to integrate it.
The point of pacing a session or fight is to never have the players walk away burned out or thinking that it was a “nothing” session. Even breather episodes, which are troughs in the context of a campaign, have their own crests, and even the final session needs some trough to give players a chance to wind down. It’s easy to forget about controlling the excitement level for just a few hours of play, but working on it will help you have memorable sessions, which is a good step toward a memorable campaign.
Unless you specifically intend for your sessions to be forgettable, but that’s so far out of Charisma-based DMing that I’m not sure I can help you.