Use dialogue to show, rather than tell, the reader what is going on. A conversation between characters can tell a reader what is happening in a more interesting and often faster way than pages of description. Robert Bacon's article "Writing Tips for Novelists" says, "... dialog automatically creates actions, since the characters are speaking." The article also suggests reading aloud the dialogue you've have written so you can hear how it sounds. It's important to make sure the dialogue flows naturally since often we don't speak the same way that we write.
Balance your story by using a storyboard, advises Sara Sheridan in her guest article on the Writer's Digest blog. Go through your story part by part, looking at it as though it is a comic strip. What pieces are essential as pictures, dialog and text in order to make the story fit as a comic? This will help you focus on what your story really needs to push it along and keep the reader interested.
Chose a tone or voice and be consistent with it. Use only one tense -- past, present or future -- to avoid confusion both for the editor and the reader. Present tense is especially good if you want your story to have immediacy, according to Sheridan.
Simplify your vocabulary. Use adjectives sparingly and use the action itself to describe the events. This will help you from getting too caught up in descriptions and keep the story moving at a good pace. Look closely at how you are using words and be sure you are using the ones that best convey your meaning.
End your chapters at exciting moments. If you end a chapter on a slow note, it gives the reader a chance to put the book down.