In the field of discourse grammar, linguists have studied the construction rules of texts and how sentences within a text are bound together in order to form a single, coherent unit. The British linguist Michael Halliday was one of the first to posit the existence of a "text grammar" that overlaps the ordinary (sentence-oriented) rules of syntax. In other words: discourse grammar refers to a set of rules that extends beyond the level of the simple sentence, and deals with the way in which sentences are inter-related. Discourse must be understood here as a piece of spoken or written language (sometimes called an "utterance") that is longer than a sentence.
How should I organize and prioritize information in a longer piece of communication - whether it is an essay, an article, a speech, etc.?
Remember that the very word "text" comes from a Latin verb which means "to weave", and you must pay particular attention to these inter-sentential links for your message to be perfectly clear. Otherwise, the holes in the fabric will give your reader the impression that your text lacks cohesion, i.e. that information is not properly organized. Syntax is all about order.
Cohesion is mainly achieved through lexical means, that is, by means of certain cohesive words, used for that very purpose. These words are used to connect a sentence, or part of a sentence, with (parts of) the previous or following sentence(s). They participate in what is called "endophoric" reference (words/phrases that refer to other words/phrases inside the text). If a word or phrase (i.e. a fixed expression) refers to an element that is not present within the text, to some element or piece of information that belongs in outer reality, it is then called exophoric.