The Atheist community (for want of a better term) is probably amongst the best educated of any community in terms of the range of interests they have and particularly in the range and number of books they read. Many Atheist will be voracious readers of science, philosophy and even theology. Many will have interests in history, geography, politics, economics, travel, natural history (rather than the science of biology) and classics, and central to our philosophy of life will be a love of free thinking, rationalism, truth and objectivity.
So, who better to write reviews of the many popular religious and creationist books, as well popular science, evolution, humanist and atheist books? We owe it to potential buyers of creationist and popular theology books to write honest, considered and objective reviews on sites such as Amazon, which positively encourages them. It's worth bearing in mind that you'll be writing for people who read books and are not afraid to own more than one, so not your typical Twitter creationist.
And, of course, we owe it to potential buyers of popular science, atheist and humanist books, to be equally factual, objective and honest.
Here is a link to an article explaining how to write a book review. There are lots of others on the Internet.
Go to it good people.