Write brief descriptions of each of the main characters. Pay special attention to any powers each character has and the species to which the characters belong. A good understanding of the characters may help steer the plot if it becomes unwieldy.
Construct a rich and detailed setting. The "world" of a fantasy novel is almost a character of its own. Fantasy novels frequently include colorful and imaginative maps of the world.
Consider the main ideas or themes that you intend to express in the novel. Making the fantasy world relevant to the real world is important. Write these ideas down and keep them in mind as you construct the outline.
Write a synopsis of the plot. Ideally this will be a single paragraph. If condensing the story in this manner is proving difficult, perhaps there's too much story.
Divide the plot into sequential scenes or storyboards, as in a movie. Note who is in the scene and what happens. Software used to organize text into slides or frames is an effective tool for constructing storyboards.
Scan the completed outline. Look for scenes that don't add to the plot or the reader's knowledge of the characters. Also, look for areas where more detail is needed.
Look more closely at the scenes and actions mapped out in the outline. Determine whether the themes of the novel have received enough emphasis. A novel has to be more than a series of events.
Adjust the outline to incorporate any changes and reassess. At this point, think about how to divide the entire plot into chapters. If necessary, begin outlining the novel at the paragraph level.
Keep the outline handy as you write the novel. Stay true to the world you have created and its rules. Refer to the outline when necessary to be sure that plot and characterization remain within established parameters.