Singing lullabies to your child can help with developing an interest in sounds and music. They will quickly have a favorite.
All about crawling
Cardboard Box Tunnel. Make a tunnel out of boxes and encourage your child to crawl through it to you. Play peak-a-boo or maybe roll balls through it. http://www.kidspot.com.au/Baby-Baby-development-Fun-crawling-games+5072+44+article.htm
This activity is simple. Find a box and wrap it with wrapping paper and give it to your child. Let them figure out how to rip it and open it on their own. This will help their small muscle control and coordination.