I always start with Beginning series books by Wrox.
They are red in colour, with human faces as the cover page. Hard to
miss, but they are quite expensive.
Another series of books which I start with is The Complete
Reference of XXX (XXX is the subject).
White in colour. They are usually very thick.
If I can't find such books... I will just take any book, read
through the first few chapters. If it's easy enough to understand,
then I will use it.