Choose something you're interested in or a hobby you know something about. Tell how to go about tracing your genealogy, the best kind of fishing rod and how to use it, or why your favorite football player is so successful in the sport. Because you have personal experience or knowledge of the subject, you may be able to write an essay on a hobby or interest without doing research, or by doing just a minimum amount. You are likely to write an essay that will hold your reader's attention, since you will communicate your passion for the subject to your reader.
Find a problem or question that has at least two reasonable answers, and analyze which is the best one. Write about the best way to keep weeds out of your garden, or the best way to study for a test. This type of topic is often easy to write because there is a natural organization in the format: you outline the problem or question, and then you tell of possible solutions or answers. You can compare two or more possible answers, or just give the best one.
Talk about what causes something. It might not be something you can be sure of, but you can speculate and analyze and cite research supporting one idea or another, sch as the causes of sudden Infant Death Syndrome, the hole in the ozone layer or global warming. Pick a topic that has good support for two possible causes, or that has several interesting studies that give good evidence. Talk about historical data, such as the rise in the incidence of autism or the reduction of incidents of SIDS after the "Back to Sleep" program was introduced.
Knock down a popular myth or try to solve a mystery, such as what causes autism or why sharks never sleep. Explain the myth and why it might seem to be true, then show evidence that shows that it is not. Or explain why the mystery exists, such as how anecdotal evidence may lead observers to conclude that immunizations cause some cases of autism, but and then show research that shows the link is likely to be coincidental. For a mystery, you may want to provide more than one likely scenario and leave the conclusion to the reader.
Explain a relatively new phenomenon or activity, such as rap music or extreme skateboarding. Tell how it became popular, and explain the various elements involved. Assume the reader knows nothing about it, since it's a new phenomenon she may not have heard of. The Internet may be your best source for information on topics that are relatively new.