Choppy sentences and what to do about them — terrific handout from University of Minnesota.
The short answer: combine short choppy sentences into longer smooth sentences via sentence combining.
And see: Avoiding primer style.
For those of you who don’t know what the phrase “primer style” refers to, here is a page from the reading primers used in the 1950s. These very simple books were created because children were supposed to memorize words instead of sounding them out.