1. Sign up as a book reviewer! Plenty of authors offer up their books for free if you are willing to do a quick review. I, for one, offer anyone who wants to read and review my books not just one free book but all of my books. Pick a book. Read it. Review it. Ask for another one.
2. Sign up to Kindle Unlimited! You pay a monthly fee but you can read books pretty much all the time. I have KU and I love it. I'm constantly downloading new books.
3. Sign up to Audible! You get one free book a month and the best bit? You can listen rather than read. This is great for when you want to go to bed.
4. Join a free book site! There are quite a few on the internet, like eHarlequin. . I've never really done this one but it might be worth a go.
5. Smashwords! Some books are free on Smashwords as it allows the reader to choose how much to pay for certain books.
6. Writing as you go sites! There are plenty of websites like Wordpad or Inkett or Fictionpress.