I use a method based on www.amatuerlogic.tv episode 3.
I have also used the one you find when you Google RV WIFI BOOSTER (it's a PDF file you print on heavy card stock, cut out, foil cover one piece and drop over an antenna) I have seen some interesting designs based on a kitchen strainer.
All work The first two I mentioned seem to be the best.
I'd like to try mounting the Wi-Fi modem in front of a Satellite dish but so far that has not worked as well as I'd hoped when I tried it, Need more math (And another dish) Before I try again.