Digital Gee

I had the LBS install new pads about a month, six weeks ago. They work just fine, but now, the tension in the back brake handle has gotten looser, and the back brake is actually just slightly rubbing the wheel every revolution.

I know this is simple for you guys, but remember I was born mechanically challenged, so help me out here. What do I have to adjust -- the little set screw that determines how far away the pads are from the wheel, or something up by the brake lever, or something else? I'd really like to know what to do so I can save a trip to the LBS.

While I'm thinking of it, do brakes require fiddling every few weeks, or is this an anomoly?