Although publishing a non-fiction or reference book in your own business field is the most obvious choice to increase your authority, there are other possibilities. If you write poetry, fiction or children’s stories, these are also perfectly valid genres and, depending on your reasons for publishing, may serve your purpose just as well. A well-written, successful novel may raise your profile as much as a non-fiction book would; a professionally produced poetry collection or illustrated children’s book may catch the public’s eye and generate just as much visibility, as well as making you stand out from the crowd. Be aware, though, that toilet humour or controversial topics such as politics can be a risky choice!
To increase your authority, you don’t necessarily have to publish in your own field: the important thing is that, whatever type of book you publish, it should reflect the quality and professionalism that you want to show to potential clients.