This book is not just about mistakes writers make but about things they tend to neglect. However it will not tell you "How To" create a world. That is still up to you but the most important point is to create an abundance of living beings and all they need to survive in a believable way.Generally, this book is aimed at writers of SF or Fantasy. Of course it also is of help in any other genre if you want to avoid mistakes in the details [Nothing is more annoying than a medieval person walking through fields of maize (Columbus imported maize from America; the first fields in Spain were cultivated in 1525) or an east side window showing a glorious sunset (the sun sets in the West)].