It’s really very easy. Buy her book.
Don’t just buy her book (though she’ll love you forever for it). Let her know that you like it. You’d be surprised how many people will take the time to complain to an author about every little thing they disliked in her book and how few bother to let her know they enjoyed it. Writing’s a tough business, and you have to do it for love (because in this recession, there sure isn’t much money for most of us). A few kind words from a reader can make all the difference in an author’s day . . . or week.
So next time you read a book that you enjoy, drop a note to the author. Tell her so.
Then make her really happy, and tell everyone else so, too.