There are a slew of bad books and bad authors to avoid. This forum has several posts dedicated to that. There are various types of magic practices, so making one list of what is bad would be difficult. Knowing what you seek before you seek it will help, understanding yourself and your own current beliefs will help, and most importantly thinking about the information you read will help.
Not knowing who you will come across as an author, and certainly not knowing all of them, my advice would be: Read the Author's biography. Read the Introduction, the bibliography of the book and read the Preface. Those will give you a good idea of what the book is about and who the author is.
You can google authors and book titles to see what the reviews say about them. Remember that everything is written from the authors perspective and understanding, if it varies widely from your own, it will probably be of little help to you.
I am a witch but I am not Wiccan. The vast majority of the books I have, regardless of what the title may say, are written by authors who purport to be Wiccan. This can cause issues for many, especially if they do not know what that are getting. I knew what I was getting, with extra research, some critical thinking, and a healthy dose of common sense I have been able to find gems of valid information to my practices from some unlikely sources.