The classic 5 paragraph essay is the easiest format to follow. The first paragraph starts with an interesting first sentence. It covers the general idea of the essay and finishes with the thesis sentence, which states the main or overall idea.
Paragraphs 2 through 4 each start with a topic sentence that the rest of the paragraphs further explains.
Paragraph 5 summarizes the essay. There can be more body paragraphs but dropping to 4 paragraphs total would not work as well.
This is a very basic format and I remember being taught this in school and seeing a great improvement in the quality of essays written by me and my classmates.
For further information, do a search for "5 paragraph essay" and find a link like the following: http://grammar.ccc.commnet.edu/grammar/five_par.htm