Hi I've been studying the entire Hooktheory 1 book and I really loved it. There was one thing though I noticed I kept struggling with: in almost all your examples you start your chord progressions with the I chord, which in that case makes it easy to identify the root key of the progression by ear. However a lot of progressions that I like do not start with the I chord, but let's say the IV chord for example. In that case I'm having trouble hearing the root key correctly. I tend to think the scale degree 4 is the root (cos that's what the loop resolves back into). Is there a trick how to focus on the actual root key and hear it correctly?
This is sometimes a bit tougher, but usually even when the chord isn't the first chord in the progression it should still have a strong "home base feel". Try to listen for when your ear feels like a progression "is over". Many times a progression will return to the home base chord to resolve tension. This release of tension is often a strong effect and can be readily identified with practice.