Writing a coherent essay on a chosen topic requires forethought and clear thinking. Here are some tips that may help:

1. Choose a "theme" for the essay. It may be ingenious or matter-of-fact; but the failure to organize around a theme will surely detract from the coherence and force of the essay.

2. Organize your thoughts before you begin writing. Create an outline of main points or topics. Give some thought to how to best transition between the topics.

3. Write an introductory paragraph that tells the reader what the subject of the essay will be, including the major elements to be covered. Be succinct. For example:

The Constitution of the United States established a system of government in which three separate, but equal, branches exercise power, sometimes in the same fields, often in completely different fields. The interplay of these three branches over time has evolved "checks and balances" that has promoted a stable and enduring system of government.

4. Unless your are a practiced stylist, it is best to write clearly in short declarative sentences. Avoid vague adjectives.

5. Be sure to fill your essay with as much detailed relevant information as you can in the time provided.

6. Don't drop the reader off a cliff. Write a brief conclusion.