It's as simple as pie:
1. Obtain a wreath form. The article suggested a Styrofoam one which you would then wrap with fall-themed fabric. I opted for a straw wreath (about $3 at JoAnn's) which I wrapped in wide brown ribbon and decorated with a few oddments I found in my decorations box.
2. Cut out a bunch of simple leaf shapes from sturdy cardstock in several fall colors. (I lucked out and found 12x12 sheets on sale for $0.20/ea instead of $0.69!) Make a virtue of necessity: you're going to want to fold the paper in half when you cut to get a symmetrical shape. This actually gives the finished leaf a nice 3D look!
3. Set them out with some good pens and have everyone at your Thanksgiving gathering fill a few out with something they're thankful for. Then pin to the wreath with a sturdy quilting pin.
We got a lot more participation after this photo was taken and our wreath was quite well filled out by the end of the party. I plan to make this a tradition - hopefully we'll be able to take a few minutes each year to review what we were thankful for *last* year!
My aunt also suggested that it might be fun to decorate the wreath and leaves in Christmas colors so you could have a decoration that you want to leave out all season long.