During editing, I've found that my plot is sometimes slow. Here are some tips that have helped with that:
1. Group events together: If possible, have a subplot intertwining with the main plot. If more than one event can occur in a chapter, that adds tension and action.
2. Take out extra dialogue: Dialogue that isn't pushing the plot forward is just wasting page space
3. Remove events with similar settings: Do your characters always sit around in someone's room or in the same coffee shop or at work? Take out any repetitive scenes to tighten up the story.
4. Write a one sentence summary of something important that happens in each chapter. If you can't think of one for a part of your book, maybe it's time to cut it out or add some trouble for your MC!