Several years ago I got an idea from Jessie Wise, either from a workshop tape or from The Well-Trained Mind (I can't remember which). The idea is for them to have a list of various types of books that they are required to check out each time. They may, of course, check out books that they want, but they must choose at least one from each category. It keeps them reading different genres and styles of writing, and exposes them to a wider range of interests. I took her "categories" and typed up cards on cardstock which the kids have carry with them:
This has been very effective over the years. In fact, Kyle commented today that he was glad he got a book about Thomas Edison for his biography, as he has already learned some very interesting facts about him (and I know he wouldn't have naturally gravitated to the biography section on his own.) Bethany got a couple of Christmas craft books that I know she'll enjoy, even though she would normally hang out in the fiction section.
Something else I have found helpful is having a library clipboard. I used to use a plain one, but then I had to get the kind that has storage in it because mine was getting too full. On/in my clipboard I have a copy of the Sonlight books arranged in the Well-Trained Mind sequence, the kids' personalized booklists from Bookadventure.com, and a well-worn copy of Honey for a Child's Heart by Gladys Hunt. Taped to the clipboard, under all of the papers, I have a copy of the Dewey Decimal Classification System, so we can find the different types of books on their lists more easily. Our library gives you a printout of what's been checked out on each card, so I keep that clipped on top so I can keep track of what we have out.
Since we've been known to cart home loads of books, I have a designated area of the house where all library books are kept- at all times! Occasionally one will end up on the nightstand next to a bed, but I'm a nut about making sure they keep them downstairs with all the other library books. Fines from lost or misplaced library books drive me crazy because we could've just gone and bought the book! (Besides, before I got my "system" down, we paid enough fines that they could've named the new branch of the library for our family.)
Something else we get each library visit are travel videos. I have found those very handy to put in while they are eating lunch or we all need a break. It's been a great way to "see the world" and has really expanded our horizons.
I hope that you have an accessible and easy-to-use library system where you are. It's been one our favorite hang-outs!