The best map reading guide I've come across is available from Geoscience Australia. It is simple and to the point, and worth buying as it comes with a plastic map card with 4 different map scales. This increases precision when taking grid references off a map and entering them into a GPS unit.
Geoscience Australia have kindly made the map reading guide available on the web at: http://www.ga.gov.au/image_cache/GA7194.pdf