The only way to become better at reading is to read. As for spelling, practice and read more. People get better at things like spelling, grammar etc as they read and practice.
There are so many variables that make up my favourite fantasy book. Good characters and plots for one. I like some magic, but not lots of it. I don't mind if it's set in our world or not, but I love different worlds. Mythical creatures are amazing, but it won't make or break a book. As for...