Pretty straightforward. Cut off strips with some scissors - take your time and make sure that you have a good coverage - just needs to be one layer - overlap edges of each of the strips so that you get connectivity between strips. Overlap the edges of the cavity slightly as well so that when you shield the cover you get connectivity. DB likes to put a line of solder along the edges to ensure that he has complete conductivity - I use a multimeter to check that I have conductivity at a couple of points. Given you are looking for a faraday's cage effect, it shouldn't matter if there is a small gap somewhere.

Be careful though - the edges are very sharp and it's easy to give yourself a nick.

Hope that helps.