The best writing says the most with the fewest words. Make sure the reader can't misunderstand what you are trying to say. Prune - Delete repetitions because they bore the reader. Change repeated words to other commonly used words when you want to address the same thing in the next sentence. A thesaurus is helpful for this, and many word processing programs offer this service on the computer toolbar.
Word repetitions are only useful for deliberate emphasis.
Different subjects are best addressed in different stories. The ending paragraph or paragraphs should clearly signal the end of your story. Save a little humor or bang for the ending. Compound sentences should be broken down into short, easy to understand sentences. One or two word sentences create interest if not overdone.