I started using gelatin after I read New Brewing Lager Beer. I basically follow the procedures in the book. Chill the beer to below 40F. Add 1gm of gelatin to 2oz of cold water per gallon of beer to a small pot. Let it sit covered an hour. Gradually heat the mixture to between 150F and 160F. Stir it to mix the gelatin and water thoroughly. Pour the gelatin mixture into the beer. Mix the gelatin into the beer by gently rocking the carboy/keg for a couple of minutes. Then the book says to let the beer sit for 7-14 days.
I typically vary my procedures slightly. I'm sure their is an exact recommended temp for the beer before adding gelatin, but my refridgerator usually sits at 38F-40F most of the time when I don't have the temp controller attached, and it works fine. Often times I will use the Knox packs just for convenience. When I do, I just mix one packet (7gm) to a pint of water for simplicity. I typically chill my beer and rack it to a secondary. Then I add the gelatin, put the airlock in, and rock the carboy for a couple of minutes. I let the beer sit until it's clear, which usually only takes 2-5 days at the most. Then I transfer it to the keg and carbonate. I get clear beer from the first pull.