Using different types of sentences will make your story better.  It will be more interesting for the reader if you write in all three types of sentences.  The sentence types are attached as a picture if you don't know them (I didn't create the image).  Writing in different types of sentences will considerably improve your writing and will help with how you want to set the scene.  

The amount of words you use in a sentence will help too.  Short sentences are good to create tension, whereas long sentences are more detailed and make the scene more relaxed.