I used this book in the 1980s when I was a green trainer, training Texas state employees to use their first computers. And it's excellent: concise, friendly, and full of useful tips and exercises. The book helped me define my teaching goals, set training objectives, and recognize what student success looked like.
The book has since been revised, so you may prefer to get the current, third edition. However, the fact that this book went 13 years between revisions speaks well for its durability, and a PBS copy of the second edition could help you decide whether to invest in the third edition.