There’s a relatively small, but very steady demand for books on painting portraits and this 1990 guide, reissued in the North Light Classics series, is definitely worth a look.
The first thing to say is that it’s an American publication, so the work included is pretty saccharine and won’t always be to European tastes. Nevertheless, the author is a master of her subject and there’s no arguing with the quality of the results or the depth of the explanations.
The book is well structured and progresses from exercises that work on the proportions of the head to handling the eyes, nose, mouth etc. This is necessarily quite slow work, but fundamental, and the attention to detail here pays dividends later. Further chapters deal with the body, clothing and lighting in a similarly thorough way before we move on to colours and two quite separate sections on working in oil and in watercolour.
This is a book that doesn’t compromise on the quality of its instruction for a more attractive outlook and is all the better for that. If you don’t have access to a real live teacher, this is very much the next best thing.