Check out this Parabolic Template. Using just printable white card, tin foil, scissors, a craft knife & Pritt Stick, you can improve your wireless reception. The tin foil only needs gluing to rectangular section alone. Mounted to your routers aerial (or x2 or even x3 aerials) you should see a measurable increase in reception. You can use one such utility like Wicd under [X]ubuntu for measuring link strength.
I found it makes all the difference between a rock solid connection in bedroom with door closed & not even detecting a network at all! As far as free fixes go it’s pretty impressive & I might not actually need that mahusive after market aerial ordered from Hong Kong.