When you have new readers, they can be easily put off a book by things YOU as a writer does. Let's say that you have an author's note at the start which is rude, obnoxious etc- no one will read past that first chapter! You are supposed to encourage people to read your books and you are a crucial part of your book's success- if people like you, you will gain support and readers.

Another thing which will ensure that you keep your readers is to reply to their comments, you know it's just common decency but some writers don't reply to comments. I mean its understandable if you have millions of comments flooding in but if you only get like two then COME ON. I mean there are some exceptions to this rule like if there is no response to the comments e.g OMG or UPDATE! because like what do you reply to that.

P.S be nice to your readers, they are some of the most amazing people in the world. Treasure them, love them and let them know how much much you appreciate them.