Unfortunately there appear to be no tutorials on how to use Metafont, except for the information provided by Knuth. There are, though, a couple of articles on how to run both Metafont and MetaPost.
Geoffrey Tobin has provided Metafont for Beginners (see using Metafont). This describes how the Metafont system works and how to avoid some of the potential pitfalls.
Peter Wilson's Some Experiences in Running Metafont and MetaPost offers the benefit of Peter's experience (he has designed a number of 'historical' fonts using Metafont). On the Metafont side the article is more geared towards testing and installing new Metafont fonts than on the system, while on the other side it describes how to use MetaPost illustrations in LaTeX and PDFLaTeX documents, with an emphasis on how to use appropriate fonts for any text or mathematics.
Hans Hagen (of ConTeXt fame) offers a MetaPost tutorial called MetaFun (which admittedly concentrates on the use of MetaPost with in ConTeXt). It may be found on his company's MetaPost page.