Books about magic have changed over the years - hundreds of years ago, their words would have been cryptic and hard to understand, as the writers knew that their tomes would have been banned instantly if the authorities knew what was really contained within their leather bound exteriors. Today's magic writers have little to fear, but then again the magic we read about nowadays means to entertain us and not to shake the Establishment.
If you've ever wanted to write about a world of magic or fantasy, you'll first need to establish which kind of magic you want to write about - is it the J.K. Rowling type of spells and incantations, or the other sort of Magick which is interwoven with ritual, craft and Wicca.
It would be inadvisable to start writing, without doing your research first - as the aficionados of both brands of magic/Magick would be expecting a magical writer to know as much as them - or even more - about their chosen subject.
If a magical, fantasy world like Harry Potter's is what excites you, then plot your story well. Ask yourself, will it be set in the present day or in the olden times? Are your characters living in an alternative Universe - or even on another planet, such as Mars?
Whichever magical world you'd like to write about and invite your readers to inhabit with you, I wish you joyful writing times. This genre is one of my favourites to write in - along with the broad spectrum of supernatural.