What these guides contain
The commonest format is one subject worked through on several models: a book takes grey aircraft camouflage or dark yellow armour and shows the whole process from primer to the last layer of grime. A second group is general beginner's guides that walk through an entire build from opening the box. A third is narrowly focused volumes on figure painting, metallic finishes, landscape and dioramas, or building structures.
How to pick a guide
Start from where you get stuck
Name the problem first. Grainy spray finishes mean you need a book about airbrush handling and thinning. A model that is cleanly painted but looks flat means you need a weathering title. A general guide to modelling will help less in either case than a narrow one.
Match the book to the subject
Methods do not transfer one for one between fields. An aircraft is soiled lightly and in specific places, an armoured vehicle heavily and all over, a figure is brush-painted with the emphasis on facial contrast. Choose a book that works with what you actually build.
Language and readability
Much of the range is English, with some titles multilingual or in Spanish editions. Step-by-step books work reasonably well in a foreign language because the stages are numbered and photographed. The passages that genuinely need reading are the ones about thinning and ratios.
What you will need at the bench
For the same material in periodical form see The Weathering Magazine, and for the history of the machines rather than the method, reference books on real machines.