Start out by drawing your glasses on to card with a pencil and a ruler. If you don't want to design your own, you can use my template.
Cut out your templates and cut out two curved strips (as shown) which will balance the glasses on your ears. Glue these to either side of the glasses.
Cut out the eye part of the glasses using a cutting knife and a ruler.
Select some pretty paper and draw around the glasses on to the back of the paper.
I only drew around the front part of the glasses, but you can draw around the whole pair if you like.
Cut out the second glasses shape.
Cut the red and blue (or green) plastic film so that it's a little bigger than the eye holes and glue at either side, on the wrong side of the glasses.
A good tip here is to use the cut outs from the inside of the glasses to get the shape for the film.
Glue the second glasses part on top, so that the pieces of plastic film are in between the front of the back and you're all done.
Now you can wear them and look at 3D photos or just marvel at how awesome the world looks through them!