You dont want to put a variable resistance in series with the signal...
You want to make a voltage divider to ground with a 'log' pot (as opposed to 'linear')
Otherwise there is no guarantee that the full range of the pot will be used, and no guarantee that the volume will increase evenly (using a linear pot it will increase exponentially). This is how every volume knob you've ever turned is wired.
I typed "volume knob wiring" into google. This was the first result. Not to complain (Im complaining) but why do people want to wait 5 hours for a forum response when google has all the answers in the world?
http://www.stewmac.com/cgi-bin/hazel.cg ... fo/fi.html" onclick="window.open(this.href);return false;