Variety is the key. Most people write the same sentence over and over again. The same number of words–say, 8-10, or 10-12. The same sentence structure. Try to become stretchy–if you generally write 8 words, throw a 20 word sentence in there, and a few three-word shorties. If you’re generally a 20 word writer, make sure you throw in some threes, fivers and sevens, just to keep the reader from going crosseyed.