Some things are meant to be chubby: Santa, little furry critters, and snow men, to name a few. Some things are not. When choosing hamburger at the supermarket, you see packaging that indicates how lean/fat the hamburger is: 90% lean, 80% lean, etc.
Your story should be lean, too. You don't want a book that's 60% lean, because that means it has 40% fat that could, and should, be trimmed. Those spare tires and jiggling thighs are usually indicative of minute details, redundancy, and scenes that do not move the story along.
Minute details drag the story to its knees. It's like walking through a forest and hitting quick sand. You get stuck. For example, I don't want to know that the character has woken up, stretched, brushed her teeth, sat on the toilet, taken a shower using Dove soap and a loofah that she just bought yesterday at the store, and then answered a phone call telling her her husband has been in an accident. These are all details that do not give life to your story, and no one really cares to read a minute-by-minute itinerary of what we do when we wake up. What we care about is that our character's husband has just been in an accident. So get there and tell us.
Redundancy is boring, and may seem to the reader that the author doesn't believe we can hold a single thought in our head. Chapter 3 might tell us that the amulet our character has received has been passed down to the first daughter for 10 generations and safekeeping it from the evil villain is key to keeping the world safe from annihilation. Chapter 10 reminds us that the amulet our character has received has been passed down to the first daughter for 10 generations and safekeeping it from the evil villain is key to keeping the world safe from annihilation. And chapter 18 reminds us that amulet our character has received has been passed down to the first daughter for 10 generations and safekeeping it from the evil villain is key to keeping the world safe from annihilation...just in case we forgot. Does your story need to repeat itself to get its point across to your readers?
Axing scenes that don't move the story along is by far the hardest trick to master. It might be a scene full of award-winning prose, clever use of language, or just your, the author's, baby and absolutely must stay in for personal reasons. Let it go. If it's not crucial to the story, it's a jiggling thigh or a big butt. I remember reading how JK Rowling's publisher (or movie director...I honestly forget if the interview was talking about the book or the movie) wanted her to axe the bathroom scene where Hermione, Ron and Harry battle the troll. She fought for that scene, because it cemented the friendship between the 3 characters. It was crucial to the story; the friendship between the 3 characters was pivotal to the entire series. If JK had said, "But I like trolls! It must stay in!" the argument would have had no merit.
So read your story with a critical eye. It may need some liposuction in order to become a lean, mean, reading machine.