One thing I recommend is to break the entire thing down into individual scenes. A yourself the following questions for every single scene in the story.
1. Why did you write this scene?
Answering this question isn’t as easy as you think it might be. At least answering it correctly. Every scene needs to serve a direct purpose (see questions # 2 and 3), so putting something in just because you think it’s fun or cute, isn’t a good answer.
Likewise, if you insert a scene simply for character development, you best be careful. Most character development can be done within other, more complete scenes, so if you decide to dedicate and entire scene to developing a character, you better have a really good reason.
2. How does it help advance the plot?
If you can’t say “This scene moves the story forward by…” then you have to highlight it and delete it. Every single scene must advance your plot. I’m not joking. Think about yourself as a reader. What did you do when you read the seventh and “final” book of Stephen King’s Dark Tower series from page 200-950? If you contemplated suicide, it because for those 750 pages, King did nothing to advance his story and you were bored out of your mind.
Don’t do that to your readers.
Also, don’t have a flashback scene unless it directly influences–and advances–the main storyline of your novel. Don’t use dream sequences unless they are 100% relevant and never, ever, show your character doing mundane things like getting out of bed and brushing his teeth.
2. What conflict takes place in this scene?
Seriously. What conflict takes place in this scene? If your answer is “conflict?” then highlight the scene and hit the delete key.
The conflict can be subtle, or it can be great. It can be between several characters, or an internal struggle inside of one. But it must exist. To a reader, no conflict equals no stakes, which equals no interest.
Keep the good stuff.
So after you’ve determined which scenes can be cut that doesn’t you have to cut everything that took place. Say you cut a character development scene, but you have some really good descriptions there you’d like to still use. Great. Put it somewhere else.
Just always remember this: If a scene doesn’t contain conflict, and doesn’t advance the story, it’s really just filler-space in between real scenes.
So cut it out.