There are a couple of books that are important, but most can/should be sold. Spoiler: Secrets of Transference Circuits from the Crypt is important - don't sell that. In Book II, Orakur: Of Fact or Fiction is also important. Other than that, I would read every book you find, and then sell it. Some might not give you skills, but they may prove useful, like the Light Armor field guide, or whatever it's called.
There is one book that's important. You have to hold onto it until you find where to take it and get a nice reward..after you do some more searching for what's needed. But any you read and it gives you a skill, sell. If it's a child's book, sell. Hold everything else until you find what to do with the special one. You don't have to carry books with you. Find some place convenient to store them and come back later.
One small hint: doing a quest for Wendy will start you on the road for what I mentioned above.