The focus on Mabon falls on as many different aspects as there are Pagans, but I've decided to limit myself to my two favorites: The Second Harvest Festival, and Balance.
Mabon is the 2nd of three harvest festivals. The first is Lammas or Lughnasadh, which falls in the beginning of August and is a celebration of the first fruits of a traditional harvest, such as wheat. The third and final one is Samhain, on October 31, which I'll talk about at length in the coming month. The Autumn Equinox (known by Wiccans as Mabon since about 1970) is about being thankful for the harvest, and recognizing the need to prepare for the coming winter. It's also about balance--night and day are equal at the equinoxes, which symbolizes balance throughout our lives.
So how does one go about celebrating the Autumn Equinox? Mainly, concentrate on the time of year.
Decorations, for altar as well as for home, should include signs of the season: fall leaves in all their glory, gourds, acorns, corn husks, dried grasses, and so on. The colors should also be seasonal: russet, orange, brown, cranberry and the like. Fill your home with scents of cinnamon, apples and baking bread. For the menu, include local harvest items--grains, fruits, vegetables, nuts. Also wine and grapes. And don't forget the apple cider!