The two biggest challenges for this essay will be the thesis and organization.

Thesis

You will need to come up with a good thesis and thesis statement.

In addition to identifying the essay's topic, the focus of the essay should be made clear in the thesis statement. Will the essay focus on similarities or on differences? Be careful to avoid the obvious. If you choose to write on a Ford Taurus and a Honda Accord, the similarities are so obvious the reader will know them already and not need to read the essay. The differences, however, are more useful to a reader trying to decide which car to buy. A good rule of thumb: if you choose two topics that are very similar, write an essay on their differences, and vice versa.

Next, the purpose for comparing or contrasting should be evident in the thesis statement. You can choose either persuasive or informative, and that choice should be clear in the thesis statement. For example:

Weak: The origins, methods, and purposes of judo and karate are very different.
Better: The different origins, methods, and purposes of judo and karate attract different kinds of followers.

The second thesis statement is better because it provides a reason for making the contrast: the differences will attract different kinds of followers. The purpose is informative.

Weak: The Eagles of today may have the same name and many of the same band members, but they are quite different from the original group.
Better: The Eagles of today may have the same name and many of the same band members, but fame and prosperity have greatly improved their music and image.

The second thesis is better because it provides a purpose: the Eagles of today are better than the Eagles from before. The purpose is persuasive.

Once you have a solid thesis statement, you can start planning the essay: Essay Three: Organization.