Create a thesis statement that establishes your purpose. Identify your three subjects and state whether you will describe their differences, similarities or both. Mention at least three traits or criteria on which you will compare and contrast your subjects.
Compose an introduction that leads into your thesis statement. For example, "We have created a long-overdue administrative position in our company. After comparing and contrasting the top three job candidates in terms of aptitude test scores, work history and salary requirements, we should seriously consider interviewing Candidate B."
Compare your subjects using the whole-to-whole or block method if you'd like to discuss each person individually. Keeping with the example, describe Candidate A's aptitude test scores, work history and salary requirements in the first paragraph, followed by the same information for B and C in the next two paragraphs. Maintain the same order of information in all paragraphs. Use B's topic sentence to summarize how she compares with A. For example, "Unlike A, B requires less salary for the same experience and aptitude." Then use C's topic sentence to compare her with A and B. For example, "C brings the same level of aptitude and work history as A and B, but shares A's higher salary requirements."
Compare your subjects using the similarities-to-differences method if you prefer to discuss similarities and differences in separate blocks. In other words, use the first paragraph to convey A, B and C's similarities. Then use the next paragraph to describe their differences.
Compare your subjects using the point-by-point or alternating method instead if you'd like to group similarities and differences by criteria or trait. For example, compare A, B and C's aptitude test scores in the first paragraph, their work history in the second paragraph and their salary requirements in the third paragraph. If you are arguing in favor of one person, then arrange your criteria from most to least similarities and give increasingly more space to your favored person in each paragraph.
Conclude with a summary of your subjects' similarities and differences and point out how they support your thesis.