I am usually made of glass, I hang from the tree, and I am decorative, not useful.
Bauble / Ornament
People do this when they prepare their homes for Christmas.
Decorate
You place me on top of the Christmas tree. I am often a star or an angel.
Tree topper (star / angel)
Children do this to ask Santa for specific presents.
Write a letter to Santa / Make a Christmas list
I am used to light houses at night and I often hang outside buildings.
Outdoor Christmas lights
Families do this together after dinner on Christmas Day.
Spend time together / Talk / Play games / Open presents
I am made of paper or cardboard and I contain a small gift or joke inside.
Christmas cracker
People do this when they give money or help others at Christmas.
Donate / Volunteer / Give to charity
I am a plant with green leaves and red berries, and people hang me in doorways.
Mistletoe
People do this when they celebrate Christmas using music and singing.
Sing Christmas carols