Now that I'm working on my third novel, I find that I'm willing to leave out a lot more stuff.
How did a character get from one place to another? Who cares? We know they have legs, they probably walked.
How did a character learn a piece of information? Unless it's a secret, it's probably general knowledge in their locale, or maybe they heard it through the rumor mill.
How did two characters become romantically involved? Sometimes it's important to show this, other times it's enough to show they're interested in each other. Then, when we rejoin them at a later time, it's natrual they should be a couple.
A lot of this boils down to this: Don't belabor the obvious. Don't bore the reader with details she can easily assume.
On the other hand, I've read books where some important piece of business takes place off stage while the narrative follows some character at a dinner party or driving a car or something. (This especially seems to afflict the soap opera strips on the newspaper comics page, where Judge Parker or Mary Worth are always arriving on the scene right after something interesting happened.)
Here are some general rules on when to leave it out or include a scene:
- Important character development
- Fights, arguments, conflict
- Action that moves the story along
- Unusual, weird, don't see that every day
- Spatial movement. Just go to the scene where something is happening, and we'll assume the characters know how to get there. The exception, of course, is where the travel itself is important to the plot.
- Logically necessary but obvious developments. It may be important that a character, say, has a fully-stocked refrigerator, but you don't need to show us the shopping trip.
- Sex. For some reason sex is usually pretty boring to read in books. Maybe because it interrupts the plot action? Just give us a hint that it's about to happen, and then move on.
- Boring things. Even if they're necessary for the plot, try to find a way to cut a scene that feels boring. Maybe have the next scene start right after the necessary but boring scene took place, and have characters mention that it happened.
Here's a rule of thumb: If it bores you when you're writing it, it will bore the reader when she reads it.