Developing the skill of lichen identification requires patience. Most will be learned by becoming an apprentice to someone who has a good knowledge of the subject. The lichenologist’s indispensable tool is a hand lens. Later a stereomicroscope can be acquired and for more serious identification you will need a high powdered compound microscope. An ultraviolet light source will help confirm identification for some species, particularly in the Cladonia group.
Hand lenses: A magnification of 10x is possibly the most versatile. Hold the lens close to your eye and bring the lichen close to the lens; this is the best technique. The lens will allow you to see surface features on the thallus such a crystals, isidia, soredia, etc.
A 20 x lens will obviously give more detail, but they are difficult to use. Some people like to use a field microscope.
Books: The standard identification book is Lichens: An Illustrated Guide to the British and Irish Species by Frank Dobson – 5th full colour edition published by Richmond Publishing, Slough 2005. Enlarged and revised edition with many colour photographs.