Yeah I also had the same problem when I was doing my A-levels. The text book bored me when it started adding unnecessary info.
I noticed that following the specification (which you can find online for you exam board) was a god send though. Basically, it made me learn exactly what could potentially be tested.
So, say I wanted to learn a topic… instead of looking at the text book first, I would refer to the specification point and see exactly what the exam board wants students to know and at what level of depth. Then I would go to the text book and try and answer that specification point; ensuring that I knew it.
To put it simply, my learning and revision was centred around the specification. The way it is, the examiner can not test you on anything that is not on the specification so make sure you’re utilising it.