The exercises are grouped by key signature, and each key starts at an easy level and progresses in difficulty with each new page. Since each key starts at the same, easy difficulty level, work on any key signature in any order.
If you find this book starts at a difficulty level that you are not comfortable with, I recommend working through my book:200 East Sight Reading Studies forDouble Bass, available here on Amazon or through the link at Robert Anthony Publishing.
In order to avoid the book having too many pages, the foreword, instructions, and preview are available for pdf download at Robert Anthony Publishing. Additionally, instructional videos will be posted on the author's site as they are produced.