A formal outline may be useful later in the writing process, after you have written a rough draft, especially if your subject matter is complex. A formal outline closely follows the organization of your draft.
The thesis is an important part of the outline. Everything else in the outline supports it, directly or indirectly. If you also include full topic sentences, you will be well on your way to a completed paper.
Guidelines for constructing a formal outline
Sample formal outline
Sample paper based on outline
Related topics:
Informal outlines
Backing up the thesis with lines of argument