I loved many of the books already listed.
The best little girl in the world was probably my introduction to anorexia.
There was a series of books about Cheerleaders - maybe by someone called Caroline B Cooney.
Books by Jean Ure - One Green Lead very sad. Also the plague trilogy, play nimrod for him and various others.
I read many Sweet Dreams books. And also Sweet Valley High.
There was a beautiful book called something like Please Don’t Go about a girl who went to France on an exchange visit and various things that happened to her on another visit there as well.
Books by Michelle Magorian - Back Home and A Little Love Song being my favourites.
I read a lot of (and still do 😊) school story books - Chalet School, Abbey Books, Antonia Forest’s Kinsgcote books to name but a few.
Judy Blume - still have many of them very well read 
Cynthia Voigt - my favourite is Come a Stranger.
The Sadlers Wells books
Books by Dorothy Berlie - Granny was a Buffer Girl and Dear Nobody to mention a couple.
I’m sure there are many more - will have to see what other people mention.