A good thesis will outline your essay for you. This means that the subtopics and main topic should be present in you thesis so that is forms the structure (outline) of your house (essay) and you will fill in the rest of the details later.
THESIS EXAMPLE: A simple formula for a thesis is this: Thesis= Topic+ Claim (your opinion)+ Reasons (your main points). For example if I were writing an essay on whether school should be extended to 5 years instead of 4 I may write a thesis like this:
Extending schools to five years from four (topic) would not be beneficial (claim) because students should get to college and work more quickly, school is already lacking in money and resources, and extending school will disengage students further.
Making the outline
Taking the example from the thesis created above I would then create my outline of my main body paragraphs to look like this:
Introduction
1st body paragraph= Students need to get to college and work faster
2nd body paragraph= School is already lacking money and resources
3rd body paragraph= Extending school will disengage students further.