Before writing your essay, you need to consider your purpose. Is this an argumentative essay or just a description? Ask yourself what you are trying to accomplish. Look back at your assignment sheet or the instructions given by your teacher. These directions will help to answer this question.

After answering this question for yourself, realize the difference between a thesis statement and a topic sentence. They are not necessarily the same thing. The thesis statement is your overall claim or main argument summed up in a sentence. A topic sentence is the first sentence of a paragraph that tells the reader what that paragraph is going to be about (all paragraphs should be about only one topic). Your thesis statement might be the topic sentence of your introduction, but it might not. Consider what you are trying to do in your introduction. Do you need to provide some context before you state the claim that is your thesis statement? In that case, your thesis statement will not be your topic sentence.

Much of what your topic sentence will be is dependent on what your paragraph is going to say.  The topic sentence has to embrace the supporting details in your paragraph.  Without knowing what these are, being able to suggest a topic sentence is a challenging element.  For example, if you are going discuss how different qualities are present in an "ideal teacher," one topic sentence might be, "There are many different qualities that an ideal teacher should possess."  This enables that all of the details come back to this topic sentence.

Another approach would be to present an opposite point of view.  In this, you would detail the qualities that the less than desirable teachers possess and then suggest that the ideal teacher exceed this.  For example, "The ideal teacher sets themselves apart from other teachers in the manner in which they embody the highest of standards."  What might follow would be how other teachers fall short from this ideal, and help to explain how the ideal teacher reaches this highest notion of the educational good.  In the end, your topic sentence has to cradle the supporting details of the paragraph.