It has become so much a part of who I am that I feel a little bit empty when I am not volunteering somewhere. I always recommend to people to volunteer for things you are passionate about, maybe it is children's causes, animals, the homeless, the environment, all of us are passionate about something and volunteering for those causes helps it bring even more meaning to us.
If you don't know where to start, look online, or walk into any non-profit in your neighborhood and see if they need help. Years ago, I walked into a senior living facility near my home and offered to volunteer. I have been there ever since and am now on the Foundation Board of that organization.
It feels great to know that you are helping your community and helping to make the world a better place. So start volunteering, get your family volunteering, the world needs your help!