Here are some quick bullet point suggestions to get you back on track.
Does your theme have a wide enough appeal? Are you rehashing a hackneyed, well-trodden theme? Give it a twist – surprise your readers. Make ’em think!
The central character(s)
Have you chosen the wrong protagonist? How would it change the story if he/she were older/younger? Or how about a change of sex? Don’t give minor/secondary characters too much airtime. Stick to your main character viewpoints or you’ll find yourself wandering off track. If your supporting cast are just too fascinating, maybe they need to be one of, or even the central character(s) of the novel.
Too complicated? They say there are only a finite number of plots available, and most have been done before. As with the theme, your plot must find a new angle. As Celia Brayfield observes in her excellent book ‘How to write a Bestseller’ you gain a lot of respect as an author if you surprise your readers.
How about setting the novel in a foreign country, or at least in an unusual/more exotic location?
Would the novel be more gripping/interesting/just plain better set in a different period? You have the whole of history to choose from!
Chop it out! The worst offender for slowing pace is dead wood. Do you really need that scene? What is it contributing to plot/character development? If the answer is ‘nothing’, get rid of it!
Don’t lose the thread!
This is so vital. The thread must always be there, running through your story like a seam of gold. If your characters lose sight of what they’re supposed to be doing and where they are trying to get to, so will your readers.
I hope these pointers will help you inject new life into your writing. Let me know what you think!