First, do your research about an issue from both viewpoints. In any argument, there is a position "for" one opinion of the argument, and opposition "against" the stance. Take notes about the important subjects that arise in discussion about the issue. What are the most contested matters that repeat in the central arguments?
Your local library is a good place for research. Websites are also good venues to research subjects that divide people. Write your notes in "For" and "Against" order. Placing these in a column format is helpful.
Back up your arguments. Your arguments will be more valid if you provide research to bolster your opinion. Statistics and other data are important. Do not rely on one source of information for your research. Sparse research shows your opponent that your commitment to the issue is weak. Be passionate about your knowledge of the subject.
Gather your notes. Look over what you have written in the "For" and "Against" columns. Write a rough outline, using bullet points, for each of the arguments, which are for your essay thesis and against your thesis. Mind-mapping software is a handy tool for seeing your ideas in a clear and concise manner.
Decide, when you look at this outline, how your opinion for the issue best matches against the opposition. What are the strongest arguments and what are the weakest arguments? Eliminate those arguments that appeal too heavily to emotions, directly attack your opposition, and veer off the topic. However, your essay should not be bland. Use action verbs to engage your reader's attention.
Write your essay with the idea in mind of answering the opposition with the point-by-point arguments listed in your outlines. Jot down these potential counterclaims to your opinion and incorporate those responses in your essay.
Proofread your essay for spelling and grammar. Reading the essay to someone before the final draft is complete is useful to test the soundness of your ideas.