The genres you will read and the ones that you won't. If you don't like certain genres, make that clear as it will save a writer submitting their work to you. Most will send a synopsis of their book to give you an idea of what its about, but you might want to request they send one with their submission (just in case they hadn't thought about it).
Give them an idea of what you will be focusing on in your review...realism, the characters, what you liked/didn't like etc. Where will you post your review besides your blog? Some writers like you to post it on Amazon, Barnes & Nobel etc. If you don't want to do that, make it clear you don't.
If you're going to use a rating system. Explain what it means.
Look at the policies on a few other bloggers sites. It may help you to formulate your own policies.
I have mine posted on a sidebar. Go check it out!
I really like your review policy...I am currently working on one for myself.
I agree. Just be clear about what you will and won't take: genres, paper or ebook, etc. Also make sure they know how to contact you and how long it will take for you to do a review.
You can check mine out if you want. There is a link on the right near the top "Book Review Policy"