While you are still basking in the Christmas glow, please sit down and write thank you notes to all the kind people who gave you Christmas gifts.  If you did not open the gift in their presence, they should get a thank you. It doesn't need to be long.  A short note expressing your gratitude for the thoughtfulness is sufficient.

If you have kids, get them in the habit of writing thank yous as early as possible.  If they can hold a crayon, they can send a thank you drawing — with your note.

It always amazes me that we spend weeks preparing for Thanksgiving, but can't be bothered to spend 5 minutes writing a note to thank someone.