1. Share/reblog/retweet their posts about their books.
2. Visit their websites—do this frequently, and refresh the website a few times while you’re there. This will help improve their website analytics and make it easier for more people to find them.
3. If you can borrow their books from a friend or library, do so, and write a review.
4. Ask your local library to order their books! They probably won’t order a book after just one request, but with a few from different people, they’ll at least consider it. And getting your book in a library makes it accessible to hundreds of people who otherwise might never have heard of you.