|Picture Credit: http://dazcarter.com/2011/|
Unfortunately that great advice is a little vague, so I'll see what I can do to give a couple tips. The bottom line is that tips are not step-by-step instructions and there is still a lot of room to develop this art until your pacing becomes perfect for you and your readers.
1. Do not try to describe the whole picture.If a bomb just went off and your characters are caught in a stampede to get away, they are probably not going to notice that the tulips are in bloom. If they are involved in hand-to-hand combat, they are most likely not going to be aware of the gentle breeze. In short, action scenes are not the time or place for using minor details to paint a picture. Put yourself in your own character's heads and pay attention to what they are thinking and noticing. Those are the only things that should make it onto the page. Do not feel the need to make a bland statement that they feel fear. There have to be thoughts or actions going on that make their fear come to life--once you have made their fear real you won't have to state that they are afraid. It's the same concept if they are feeling excited or any other emotion in an action scene.
2. Use short sentences.Keep your sentences short. Even a one-word sentence thrown in from time to time is fine. As the tension builds, your shorter sentences will make your readers pick up the pace and will make your character's thoughts seem less measured.
During an intense scene, your character isn't going to be pondering the meaning of life--his or her thoughts will be cut back. Characters who have training in handling the situation will be more likely to shut down conscious thought and let instinct born of heavy training take over. Characters with nothing to prepare them will be more likely to experience raw emotion--potentially leading them to act in ways that make the situation worse. But whatever is going through their heads, it will not be well-thought-out discourses. It will be clipped sentences.
3. Use powerful verbs.Use the thesaurus to help yourself come up with powerful verbs, but only use verbs that sound and feel natural. If there is ever a time to use big vocabulary, this is not it. Remember, you do want to come up with ways to portray the full graphic and intense scene, but using words that don't come naturally will slow down your action.
4. Avoid using passive sentences.This is good advice in almost all writing, but it's especially true in action scenes. Always focus the attention on the person or thing that is initiating the action. Generally speaking, passive sentences do have a proper time and place in writing--but that proper time and place is not in the middle of action.
5. Watch for your personal writing ticks and remove them.
Every author has writing ticks. You may have a pet word or phrase that you find yourself repeating too often in the book (or using in every book you write). Or you may have a habit of using hyphens more than usual. Figure out what your tick is and try to fix it throughout your book. But this is especially critical during action scenes. Action needs to be as smooth and problem-free as you can make it. If your readers have noticed a tick in your writing, it will distract them. The last place you want them distracted is in the middle of a fight or even the death of one of your characters.