Steven King wrote in his epically awesome book On Writing that you should aim to take at least a tenth (or something like that) out of your story when you edit. While I'm more of an editing adder, I see the reason behind his words. That 10% of what we wrote are all the boring bits.
The things that our readers will skip in order to stay awake for the rest of the story. The bits that add no value to the story.
They all have to go. Every. Single. One.
Getting rid of some of those scenes really hurt, sometimes. Some of them might even be favorites. But if they don't add to the story and if they're just boring, they have to go.
My rule of thumb when it comes to getting rid of boring scenes:
If they're more than 70% boring, you have to get rid of them, redistributing the 30% so that they have meaning in the story. If they're 50-70% boring, you need to cut out the bits that make the scene boring.
Once your work is zzzzz-free, you'll see most of your pacing issues disappearing. As will a lot of sagging middle problems. AND! Your story will be more exciting.
Look Out for These:
1) Crit partners of betas pointing out boring parts.
2) Any parts that were dealt with earliers and that reveal nothing new that's of importance.
3) Any parts that don't fulfill a valuable function in the story. You don't have to get rid of all of them, but if the read is stalling, you might want to cut out a few of these.
How do you spot boring bits that have to go?