You can use a larger or smaller strip of paper as long as the length to width ratio remains around 20/1
Unlike most origami, you don't want to create a strong crease on the folds. If the creases are too strong, you will have trouble pinching the sides to create the three dimensional shape.
Create a fold around 2 1/2 inches from the end of your paper.
Fold again. You will be creating a pentagon, so adjust the angles accordingly.
Tuck the end in and flip your paper over.
Start folding your strip over the pentagon, making sure to keep the shape.
When you have 1/2" or so left, tuck the end in.
You should have a thick pentagon.
Using your thumbnail, apply pressure to one side until it pushes in. If you have trouble, try piching a corner. If you have short nails, you can use the end of a ruler to help push the side in.
Continue with the other four sides.