A game session is called an Episode. The ideal is that the story begin and conclude within one game session. This is not the norm for RPG's and may take some getting used to.
To help this along, we have adapted the traditional three-act structure of episodic TV to our purposes. Before we get to all of that, a few general observations are in order:
Keep It Simple
You only need an A plot and a B plot, a main antagonist, and a a secondary antagonist who may or may not be in cahoots with the main, and their minions. That's it. Sometimes the A plot is the Challenge, and the B plot is some wrong that needs righting. Sometimes its the other way around. Don't try to cram in a C plot.
On a related note, a handful of tough henchmen is going to be easier to manage than a small army of extras.
Try to leave an opportunity for each character to contribute. We know - that's a broad range of skills to cover. However, action/adventure really only has a handful of basic activities. If you include a variety of each in every episode, you should be covered.
- A Fight Scene: A good fight with reasonably matched opponent. If there's some good reason for the fight, that's even better.
- A Chase Scene where the cast must either chase after or flee from something.
- Breaking and Entering or however the cast finds their way into someplace they are not supposed to be, or out of someplace they were not meant to leave.
- Awkward Social Situation where characters must charm (or lie) their way into something good, or out of something bad, or must face questions they don't want to answer.
- A Mystery to Solve: be it a puzzle or a riddle or a whodunnit, or a "what the !@#$ just happened here?" moment.
- Recreation: some free time within the episode where the cast can see the sights, go shopping, build something awesome, or just run amok until they accidentally generate a C plot.
You should be able to get at least three of those into any episode, and four or five into most. An episode with all six will be the highlight of the season.