How do I analyse/annotate my books better

Recently got really back into reading, and i've been picking up more books! which is great obviously, but i dont really just want to read purely for entertainment anymore, i want to really understand the more gritty parts of the book, like really try to understand the themes and the message the author is trying to say. I also want to try to a hand at annotating my books as well, please help!

For example I'm currently reading a clockwork orange, and i just got up to the bit where he was put in jail and found out georgie died. I want to try to figure out why his dreams were important, why the author self inserted his book into the novel ( you know where they broke into his house and ripped up his manuscript) i also wanna try to figure out the importance of georgie, and why he got killed off. Its weird, i guess i can recognise patterns and know when something is important, but i just dont know why!

I'd really appreciate any help, thankyou!