If you know the main points you want to make, you may want to start with a summary paragraph that sets out those main points briefly and acts as a takeoff point for your essay. Such a draft paragraph can give you momentum. Here is an example of such an opening paragraph from a noted sociologist. This kind of opener serves as a thesis paragraph to help you focus your writing as you work;

The social problems of urban life in the United States are, in large measure, the problems of racial inequality. The rates of crime, drug addiction, out of wedlock births, female headed families and welfare dependency have risen dramatically in the last several years, and they reflect a noticeably uneven distribution by race.[…] Liberal social scientists have nonetheless been reluctant to face this fact. Often analysts make no reference to race at all when discussing issues such as crime and teenage pregnancy, except to emphasize the deleterious effects of racial discrimination or of the institutionalized inequality of American life. (William Julius Wilson : The Truly Disadvantaged)