I feel like More Easy Pop Lines doesn't align quite as well as the first book. Just go through the books in the order the exercises and songs are presented.
Song Book 2 demonstrates all kinds of principles introduced in the method book. For example, shifting on open strings, triplets, and shuffle feel off the top of my head.
For me, I found Song Book 2 pretty tough. And worthwhile.
Okay cool, sounds like I will just have to get started on book 2. And songbook 2. And order songbook 1