Any Table or Figure you present must be sufficiently clear, well-labeled, and described by its legend to be understood by your intended audience without reading the results section, i.e., it must be able to stand alone and be interpretable. Overly complicated Figures or Tables may be difficult to understand in or out of context, so strive for simplicity whenever possible. Figures include graphs, diagrams, photos, drawings, schematics, maps, etc. Graphs are the most difficult to format and will be dealt with here. Hints on presentation of other figure types can be found in most style manuals.
Tables are lists of numbers or text in columns, each column having a title or label.
For course-related papers, a good rule of thumb is to size your figures to fill one half of a page. Your reader should not have to reach for a magnifying glass to make out the details. Most often your choice should be black and white only. The rationale here is that if you need to photocopy or fax your paper, all the information conveyed by colors will be lost, which will diminish the effectiveness of your work. For a poster presentation or a talk with projected images, color is often very helpful in distinguishing different data sets.