Write the action before the reaction.
Unlike the other "rules," this is one you really don't want to play with. In real life things follow a logical order. In our fiction--which represents a slice of life--we should follow that order.
This is not rocket science. All the same, it's easy when you're fingers are flying over the keys to write a reaction before an action. You may be visualizing the scene in your head, but all the reader has are your words to help him "see" the scene. If you get this sequence backwards, it's not that the reader will always understand what exactly you did wrong. It's that the power of the scene is diminished because the reader isn't able to visualize and "feel" the action as well.
She jumped when the rock hit the window.
Fear uncurled in her stomach as she listened to the coyotes' howls.
You could correctly rewrite these sentences many different ways, as long as you place the action before the reaction.
A rock hit the window and she jumped.
Coyotes howled near the edge of camp. Fear uncurled in her stomach.
Take a look at your manuscript. If this is the first time you've been made aware of this rule, you'll probably find a few backwards sequences. And even if you have been aware--these guys can sneak up on you.
Read Part 10