When promoting your book, comparing it to similar stories with which everyone is familiar can help find readers who will like yours. Of course you have to do this is a way that’s not arrogant or could get you in trouble for infringing on copyright laws.
Nonetheless, if your book has similarities to the Harry Potter series, readers who love that series might be delighted to find another source of fantasy. There’s a risk, however, because if you fall short when they can’t find adequate parallels, their disappointment may result in a rather brutal review.
Thus, weigh the pros and cons carefully before using this method. A safer approach is to simply refer to some of the elements your story has in common with a popular series or movie. Sometimes you get lucky and a reviewer makes the comparison for you, in which case you can quote them and let any ire at possible deficiencies fall on them.
Marcha's Two-Cents Worth 
A fellow author I shared a book show booth with suggested this. She wrote middle grade fantasy and thus had a sign that said, “If you like Harry Potter, you’ll like so-and-so!” I’m not sure what to compare mine to other than saying my series is a cross between “Lost in Space” and “Star Wars” or in the case of Thyron, “A cross between ALF and Audrey.”
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This is one thing I fail to do. Mainly because a couple other people have compared my Sea Purrtector series to Warrior Cats…. I tried to read that, but the similar names, etc. were confusing. However, the series IS from the point of view of cats.
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