Find out how to construct and evaluate arguments, and many more writing related topics from the Critical Thinking Web. This site also contains practical exercises.
Check this Overview on How to Write an Essay, which will provide you with information on the specific steps in the writing process: information gathering, planning, writing, editing.
Free online courses and language tutorials are offered by the St. Louis Public Library (SLPL). The courses include subject areas such as Computer Applications, Writing and Publishing, Web Design, Graphic Design, and many more. Courses run for six weeks and new sessions begin every month. If you do not have an SLPL card, now is the time to get one!