I was thinking about writing a book to make some additional money and I wanted to identify a topic that would sell. Any suggestions on how I find such a topic?

One of the things you can do is go on Amazon and look at the category you are considering writing about and see what books are already in that space. Also look at their sales ranking and how many editions of the book that is closest to what you want to write about. If most of the books in that category are first editions and the ranking is not high you may want to consider another category.

I think you may want to consider looking at it in another way. Rather than trying to find a topic that may sell you should consider focusing on a topic that you are passionate about or you are an expert in. Part of the challenge in selling a book is the credibility and the experience of the author. If you have no experience in the topic you are writing about you may have some challenges selling your book.

I agree with the other comments mentioned here as well particularly the comment about being passionate about what you are writing about. One of the things you should consider is doing a keyword search for the book topic you are looking for. Not only will you get some ideas on what people are searching for but you could also come up with a title that could show up high in the search rankings.

I read an article on how to write a book awhile ago and one of their suggestions which I thought was great is to find a classic that you really enjoyed reading and you know was a great seller and change it. By changing it I do not mean plagarizing it I mean totally change it. Change the characters, if it was set in the 1900s change it to the 2000s, if it was a romance novel change it into a mystery etc the only thing that you do not change is the theme of the book that is what has made it successful.

Great idea Redc thanks!!!

Writing a book isn't an easy task.It needs lot of hardwork and homework. Writing a book is a skill altogether.With retrospect,the current trend is to write books on "tools of the trade".You can try your hand at writing on the tools required to be a successful businessman,entrepreneur or some tips on marketing,etc.This not only fetches you additional money,it also provides inputs to yourself.

Best of luck.