It should also motivate the reader to continue. It should state the nature of the problem studied. It should outline the manuscript's major substantive contributions and organization in a way that promotes accessibility to casual as well as serious readers. Indeed, if there is nothing novel or instructional, in, say, a proof or line of mathematical reasoning, then one should seriously consider excising it in favor of a brief remark or relevant citation. For example, anything in the body of a manuscript likely to divert attention from the current focus of the storyline should be omitted or put into appendices.
Appendices are also often appropriate for the details of algorithms and proofs.
Technical terms and mathematical notation are, of course, frequently essential for precise communication or access to known results in science and mathematics. Try to keep all notation concise and consistent. Figures and illustrations of all kinds are encouraged because visual thinking is powerful and efficient. Graphs are usually superior to tables of numbers. Making a special effort to enhance a new manuscript's readability is a good investment of the author's time.