I started buying books and read to my son when he was about 4-5 months old. Mainly board books with flaps, like the Spot series. Read to him 3 times a day - before morning nap, afternoon nap and bed time. Morning and afternoon will go through about 4-5 books, whereas bedtime around 2-3 books. Usually would hold 2 books in front of him and let him choose.
But nowadays, his attention span gets shorter, sometimes half way he would lose interest and turn/crawl away. He also bites and tears his books, will pull the book away and tell him no.