Scenes grow from uncertainty.
When you’re starting a scene, establish the following two things as clearly as you can:
(from here, Starting Scenes)
As GM, film editor is one of the hats you have to wear. Things happen offscreen in movies all the time, sometimes because the editor is terrible, but more often because the scene in which they would have happened wasn't dramatic or important to the overall plot.
You also have an advantage that movies don't. You can have things "happen offscreen" but your audience will know they happened anyway because you're all there at the table talking about it.
The difference between offscreen and onscreen, for you, is that "offscreen" is basically table banter, people talking about what their characters are capable of and what general direction the plot is going, and "onscreen" is when you actually take steps to set the scene, describe surroundings, introduce new characters.
An easy transition point between the two is that the camera starts rolling just before dice hit the table. If you never get to the point where actions are sufficiently in doubt that dice enter the picture, it's not a scene.
Forgive this because it's not a clean dodge, but let's suppose a space adventure is happening and there's a sudden Imperial blockade dead ahead. You start asking about where everybody is to get geared up for a big blockade-running sequence, but your Former Imperial Intelligence Athens pipes up and says, actually, intelligence ran covert ops on small unmarked freighters like this all the time.
If this seems like a reasonable course of action and the players are into it, you can probably demand a Fate Point from Athens because it's awfully convenient, and then frame a smaller scene around a single Deceive roll where Athens stands in front of a frizzed-out holocom and tries to convince a faceless Imperial stooge that it's far above their pay grade to mess with her.
Scenes also grow from drama.
So, I realize it's almost obligatory in movies for there to be a dramatic onscreen argument about whether it's right to steal Dark Stobolous's planet-cracker keys or whatever, but when a dispute arises between your players about what course of action to take, before you start demanding people form teams up and start mortal debate combat, you should ask yourself: is this an offscreen debate or an onscreen one? Is this just players shooting out different ideas for where to go forward, or is this a genuine rift between characters that's worth putting a scene around?
An easy transition point between the two is that it's real drama when aspects are involved.
If there aren't any aspects involved but people are still generally conflicted about what to do, you can:
- split the party, which is fine because you can crosscut between the action as it becomes necessary
- if it would make sense, find out what more they need to know to help them make a decision and frame a scene around that
- if it wouldn't make sense, tell them why (doomsday clock is ticking) and demand a decision from your players if they want to stick together, flip a coin if they have to
If there are aspects involved, you can pay out of your unlimited GM Fate Point reserve to have the dissonance between them (Athens wants to be sneaky, Two Blasters, No Waiting Starhound wants to storm the front entrance) do all sorts of interesting things, like splitting the party or turning into a giant shouting match that saps the party's fate point reserve and stacks consequences on them when they need it the least.
(This is assuming your players aren't arguing because they're genuinely concerned that if they don't say the right thing they're going to fail without even trying. I kind of take that as a given, but if not, do make it clear to them that you're there to see their characters take dramatic action, not steer themselves into a blind corner.)