The thesis statement tells the reader the point of the paper in a single sentence. It gives information about the type of essay to come, the topic, the writer's attitude about that topic, the importance of the topic for the reader and the ideas the writer will use to support the topic. For instance, a thesis might sound like this:
Writing an effective essay requires planning, developing and attending to detail.
The sentence indicates the type of essay (process), topic (writing process), attitude (process must be followed), why it's important (effective essay result) and the specific concepts to come (planning, developing and attending to detail).
Think about the overall point you want to make; that is the idea you should include in the thesis. Establish the type of paper you need to create. You can use the same idea as a thesis for various types of essays. Consider:
McDonalds is the perfect place for a child's birthday party because of the service, play space, smells and sounds. (This would make a good description.)
Setting up a child's birthday party at McDonalds requires planning, cash and patience. (This would make a good process analysis.)
McDonalds seems like the perfect place for a child's birthday party until parents discover Sesame Avenue, which costs less, has more space and contains more activities. (This would make a good comparison/contrast.)
Place the thesis at the end of the introductory paragraph.
The paragraphs that follow the introduction, the body paragraphs, should each begin with a topic sentence, a single sentence that explains the point of the paragraph. For the body paragraphs that follow the writing process thesis above, the first body paragraph might start with this topic sentence:
Planning is the first step in writing a good essay.
The reader understands that this paragraph will focus on this one issue from the thesis: planning. The paragraph should include specific details that relate to this single point, such as how brainstorming can help a writer come up with ideas and outlining can help with organization.
Topic sentences must also show the reader how the concepts in the upcoming paragraph support the thesis and relate to any previous information in the essay. The second body paragraph in the writing process essay might begin with this topic sentence:
After planning, fully develop the ideas to create strong content.
Here the reader can tell what I will focus on (development), how it relates to the thesis (strong content makes a good essay), and how it connects with the previous idea (after planning, so this is the next step).