As a writer you have to lead the reader through a story that may cover a lot of ground and move around from topic to topic. One of the best ways of bringing the reader with you is to limit each sentence and each paragraph to a single subject. If you think of each sentence and paragraph as a box or room that contains one sort of information, this will enable you to do this.
To take the reader from one subject to another, begin each paragraph with a few words that indicate what it is going to be about or what direction you will be taking the story.