I have a book from the States called Real Essays, Writing for Success in College, Work, and Everyday Life.
http://www.amazon.com/Real-Essays-Readings-Writing-Everyday/dp/0312648081/ref=pd_sim_b_2 (mine is a different edition, but the same book).
I highly recommend this book for anyone who is teaching, or wants to learn, basic writing skills, starting with essays. It is basically what you would use if you were in a remedial sort of writing class at a community college in the States. They start with the real basics -- how to write a thesis, give support. They also go through all the different types of essay writing -- expository, descriptive, process analysis, etc., again with step by step guides and loads and loads of examples. I use this with my high school students and I feel like it has helped them loads, particularly with structure. For someone self studying, something like this with lots of examples would be perfect.
This is assuming he/she already has good basic English skills and is looking purely for a writing course.