Writers get less fan mail than most readers imagine. They spend their days largely alone, crafting their work and putting in all sorts of details and care – but it’s rare that they hear from their readers that someone got all that. A thank-you letter has more value than you can imagine. A thank-you letter is equally valuable for the letter-writer, though.
When you put in words exactly why you like someone’s book so much, how it specifically helped you or inspired you, you recognise more clearly what makes it so good. That’s a lesson which will repay you richly as you work on your own book.
Have a look at your bedside table and in your bag: what books have you just read that you enjoyed? Why did you enjoy them? Pull out a pad of paper and write a letter to the author, thanking them. Send it care of their agent or publisher, rather than trying to mine their personal details. (That’s a courtesy they’ll also appreciate.) Before you do, though, make a copy for yourself. You’ll want that insight as you work on your book.