First let me say that I can't believe that a booklet written in 1979 is the best and most popular book on Amazon for rock tumbling! The booklet is well written but may prove a little hard to get through for those of us in the attention-deficit age who are used to books which describe everything for us in bold fonts with call-out boxes. This is a booklet you have to actually read, like a book, to get the information out. It took me several sittings to get through and I had to go back and use a highlighter to call out the salient points. That being said if you have some patience the writing and instructions are quite clear.
One drawback to the book is that the author describes two methods for tumbling -- the "popular" or "conventional" method, and then his method which he admits is a bit perfectionistic, so you are left a bit confused as to which method to use. His technique also involves using a grit called "saw wire grit" which I have been unable to find (please feel free to comment if you can find it). Additionally, his "recipes" for tumbling are based on a large (12 lb or so) tumbler, not the 3 lb one you get in most beginner kits, so you would have to convert them (I just used the recipes that came with my tumbler).
Finally the jewelry section is extremely dated, in my opinion the jewelry in the book is hideous :-) but that's just my opinion. But staggeringly, if you buy a rock tumbling kit today the jewelry making accessories (key ring, tie tacks (like anyone uses them anymore!), pendant bell caps) are exactly the same as those used 30 years ago. So in my opinion you would do better to drill your stones or mount them in another fashion.
In summary, a very helpful reference which I have read through twice and refer to often, but needs to be supplemented with the directions that came with your tumbler, and taken with a grain of... well how about grit? :-)