Here's a simple way to make a Christmas advent calendar. There are so many calendar websites out there with templates you can print for free. Just find a single page calendar template you like and you're ready.
1. download a single page December calendar template.
2. print a second sheet or cut a second sheet of paper the size of the calendar grid or mark the calendar grid borders on a second sheet
the second sheet will be the bottom template for a single large picture or for many smaller individual pictures behind the windows
3. cut each square for all the dates in December of for as many windows as you'd like. It's sometimes nice to have fewer windows, so all the dates don't open. It gives the kids something to look forward to. This will take some time and is best done with an exact-o knife or box knife.
4. draw in your images or paste pictures to be behind the windows for each date.
5. paste the calendar template on top of the second sheet. Remember not to paste the actual windows for the dates.
Add a craft paper border to the back to make it more sturdy and look a little better. Certainly ribbons and other decorations will really make your advent calendar look incredible.