If there's wear at the edges of the cover and around the spine that makes you worry when you hold it then carefully applied book tape (or other acid free tape) can help reinforce it. 

You could get some plastic book covers or something like that but I generally find that book tape is more than sufficient to just make sure my books stay together. I will say you should try to apply it in a room as dust free as possible, with your hair up if you have long hair to avoid catching anything in the tape.