T.C.
One thing that my husband and I did was lay our son on his back and dangled a colorful giraffe toy with bells on it above his head. It had many colors for him to watch and made some noises. He would kick his legs like crazy and make noises. After we realized how much he enjoyed that, we got a play mat that had little animals that moved and played music over his face.
We also made sure to have "tummy time" at least a couple times a day. That was probably the most important thing we could have done... he didn't like it at first, but it's a very important part of babies development.
Also, keep the music and books going. You can never go wrong with that!