| First, you need to memorize the changes so you are not looking at the page. Start working on the songs/progressions at the end in the same order you covered the material in the book. Just roots, then add 5ths and chromatics, etc. This will help with memorizing/learning the progressions and is a pretty good way to develop any bass line to go over a set of chord changes, start simple, learn how it sounds and then start adding on. Ed Friedland posts here on occasion and has mentioned that the idea is to play through the progressions at the end as you learn each new approach.
Knowing where the notes are on the fretboard is also key, it should really be the first thing you learn when you pick up a bass. You shouldn't be thinking about where the notes are, you need to know them. Not just where to find one but where to find each note on each string. The approach mentioned above, starting with just the roots then adding on can help with this too, go through the songs playing just roots but move about on the fretboard and try to use them all before you start adding 5th and chromatics, etc.
Going through the book and understanding the concepts isn't all that difficult, it's being able to apply the concepts to songs like the progressions at the end that takes time to develop. If you can't follow the progressions using just the simple concepts like R, 5, chromatics, then trying to play more complex things over those changes isn't going to work. Build the foundation before you start working on the house. | 
struggling with the building walking basslines book here,please help! 
