Given that both novels, Invisible Man (Ralph Ellison) and Up From Slavery (Booker T. Washington), depict the realities of facing prejudice the most important idea to focus upon would be that of the actions of each of the narrators.
Invisible Man is a fictional piece which focuses upon the struggles of an unnamed protagonist who must come to face the fact that he is invisible in the world of whites.
Up From Slavery is an autobiographical novel which depicts Washington's struggles to gain an education and,later, educate other African Americans on the importance of education.
In order to compare and contrast the novels, one must first define the main difference: one is a true story and the other is fictional. Outside of that, comparisons can be made to define the differences both narrators faced growing up in a prejudiced nation.
One could focus on the problems each faced when it came to education, society, and personal decisions. Beside this, one could examine the positive and negative views each narrator had on their experiences--meaning did one have a more positive outlook on life and why.
To create an outline for the essay, one could use a point-by-point format for the essay. To create a point-by-point essay/outline, decide upon three differences/similarities and examine each of the stories regarding their textual support on each topic.
An outline would look like this:
II. Education for both narrators.
III. Prejudice for both narrators.
IV. Outlook on life for both narrators.