Here is an easy way to have comparable sets with the Official Guide.
Pick a unit's digit - say "7." Start with problem number 7 and then do 17, 27, 37, etc. This way you will have 10 problem sets that span the entire range of difficulty. You will be able to see if you have made improvement as you go along because the sets will be comparable. (If you just go from the front of the book to the back of the book you will almost certainly just naturally miss more questions as you go along so it is not comparable).
In order to mix it up you will want to jump back and forth a bit. For Verbal: Do for example 2 CR, then 2 SC, then 2 CR, then 2 SC, then a reading comp passage. And repeat.
For Quant: maybe 3 PS, then 2 DS and then back and forth. There are more PS on the test and more in the Official Guide, so 3 to 2 ratio. And don't forget to keep the same unit's digit (problem 3, then 13, 23, 33, 43, etc.)
Have fun!
