Create a profile with your contact information, website and any other vital information on an online reviewing site so if authors wants to contact you for a review, they know where to reach you.
Give fair book reviews so others will pay attention to your reviews. This may bring attention from both directions, from other authors and other reviewers who will recommend you to authors they know. Even if you don't care for a book, give pros and cons so people will take your reviews seriously.
Check your email regularly to see whether authors or other reviewers or other readers are asking you to rate their material or what you thought of material that was already rated. This is a form of networking that can help you get free books, especially if an author sees you consistently rating their work. That author just may pick you to read a review copy of the next release before it hits the shelves.
Contact authors after you have had a consistent and fair amount of reviews. Ask if the author would be willing to let you read his book for free, and link the author to your reviewer page. It will be the author's decision whether he wants to send the free book without charging you for shipping and handling, but it does help if the author is familiar with your past opinions.
Introduce your book club to various authors that the members all like. Although there may be some authors who are hesitant to give out multiple books to members who may not all like the book, asking for one or two review copies and stating that the other members will buy the book if a couple members like the work helps. This is also an opportunity for the author to gain new customers.