1.
If you're using books from the university library, remember that they're not your personal property, and they are a shared resource. Don't write, scribble, annotate; and really really don't use a highlighter pen in them.
2.
Make sure you return books once you no longer need them. That allows others to find them on the library shelves when they want them. Plus it means you're less likely to lose them and have to pay for replacements -- and for some books the cost of replacements can run into hundreds of pounds.
3.
University libraries generally provide a way to recall books from borrowers who have them out on loan. Don't be shy of making use of this facility. Do keep an eye on your email and promptly return any books that are recalled from you.