Once you have downloaded that stencil, simply cut out the two shapes as shown in the image below.
Step 2: Cover in tinfoil
Once we have cutout our shapes in step 1, we need to cover the shapes in tinfoil and fold them to the correct positions. The guide in step 1 will show you how to fold them. The image will explain better..
Step 3: Cutout a small hole for antenna
At this point, we will have two shapes, cutout, covered in tinfoil and folded to the appropriate position. We will need to cut a small hole out for the routers antenna to peak through. See image:
Step 4: Put it all together
Simply place your booster onto your current antenna, and that's it.
Enjoy a lovely increase in your signal strength. Remember to aim your booster in a good direction.