How and what kind of books do you read if you want to improve your language skills
If you mean, for improving your English language skills, then really any book of interest should be a reasonable option. I particularly liked Garth Nix and Terry Pratchett's writing, and the latter in particular has quite a way with language which I think would be helpful in developing someones ability in the area. The "Unfortunate Events" series by Lemony Snicket likewise might be good in that sense, since part of the style of his writing is introducing often somewhat obscure words and then explaining them...in a sense. His prose style is a bit unusual though (perhaps somewhat intricate at times) so it may or may not be to your taste.
Really though as a kid I just read almost anything I could get my hands on, which isn't a bad option for you - from "Animorphs" to "The Lord of the Rings", and much inbetween, any reading can help you develop your language abilities I specifically ended up learning to speed read (in my head) quite young because I had (when I was very young) a speech impediment which made the (at the time) usual format of "reading aloud" quite slow and difficult for me. Reading I think definitely made sure my language ability was developing, even in spite of my speech impediment (which I had speech therapy for, apparently, and got over).