If you have trouble expanding your story and making it more imaginative, this exercise and article may help (Look at Bob and Susie stories for examples).
I sometimes get so bored with a part of my story that I drop it and work on something else. If you want to avoid that problem, try and color it up by making it more imaginative. Sometimes it is really hard to get the creativity going or you in a very boring part of the story but it must be said. You don't have to be so over imaginative at a time. It takes small ideas and builds up into a very exciting and amazing tale. Lets say you have a really none interesting part in your book that you want to change. Take this paragraph for example:
 

Jill was very tired. She had nothing to do. She was lost in thought as she sat on the grass staring up at the stupid clouds. She was suppose to do a report on cumulous clouds but she couldn't get a clue on what the clouds look like. She really wanted some excitement.
Suddenly, a stranger wobbled into the meadow. He gave one glance at Jill and carried on his way. Jill sat up and looked at him. She decided to follow the stranger.

As you can see, this small section can put you to sleep. It even shows in the writing how bored Jill is. What I think is that these paragraphs need is some more colorful words, combining some sentence, and a little creativity. See the possible results below:
 

Jill brushed her hair aside and sighed. She had no clue what the clouds were doing right now. They kept swirling around in different directions. She grabbed her book beside her. Jill was trying to do a report on cumulous clouds for her school but Jill couldn't figure out what was going on. She sighed again and laid back in the grass. The wind started blowing hard and the grass in the side of the park Jill was in swayed wildly. The girl just closed her eyes and wished for something grand to happen, something exciting.
Then up the path, someone walked along. The person was hobbling along in an old gray coat and was carrying something long and pointed. Jill opened her eyes and saw the man crossing the meadow, about ten feet away from her. The man only glanced at her once and there seemed to be something special in his eye. He seemed to know much and there was a twinkle in his eye. Jill tried to make out his face but it was in shadows under his hat. For a slight moment, Jill thought she heard him mumble something but then she thought it might be just the wind. The stranger was approaching the forest at the other end of the meadow. As he got closer, the winds grew stronger. The wind was going wild by then. Jill brought her jacket around herself and sat up and stared after the stranger. She had this sudden urge to follow him. She knew better but it was as if her body was pulling her to follow, as if she was under a spell. Jill looked up at the sky. Everything was getting dark and gray. A storm was coming, she thought. Jill couldn't resist any more. She got up and followed the stranger.