Authors: keep your ego off your book covers until you are famous or have written ten books

Unless you are known for writing, con­ning people out of billions or winning Olympic medals, keep your name and portrait a lot smaller than the book’s title.

Later on, if you become famous, you can revise the covers of your earlier books.

[above] This is my approximate 35th book, and it's very personal, so it's fine for my face to grace the cover.
 
More about book covers, The Look of a Book: what makes a book cover good or bad and how to design a good one: http://www.amazon.com/dp/B00BAPV724