Carefully read the assignment and grading criteria provided by your instructor. You may want to organize your thoughts on paper. Conduct research with an eye toward not only bolstering your argument, but also toward finding real-life examples to use in your essay. Start writing once you have a solid grasp of the issue you're being asked to write about.
Use an introductory strategy or "hook" to engage the reader. Argumentative essays work best when you get to the point quickly. An effective introduction should have three key parts: setting the context, establishing why the main idea is important, and stating a well-argued thesis.
Write the rest of your introductory paragraphs, building on the "hook." Also, you should also be building toward a thesis statement by providing context.
Write your thesis statement. A thesis statement is the length of a sentence and it must be an opinion. It should also sum up the entirety of the argument you are about to make in your essay.
Write your body paragraphs with an eye for detail. Simply saying, "It is wrong" will not convince a reader as much as well thought-out descriptive examples will. Use all the facts you've gathered in your research.
Limit yourself to one major point/counterpoint per paragraph. Cite a claim, and then move on to the evidence supporting your position on that claim. Cramming more than one major idea into a paragraph will make the essay look unfocused, unstructured and unorganized.
Write your concluding paragraphs. Conclusions should be what the word suggests, "conclusive." More importantly, the end of your essay needs to provide a sense of closure. You should be able to reinforce and reiterate your thesis here. If you bring up any new issues in a conclusion, the essay will read like it is incomplete.