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.
Spotlights
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.
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.