Stand with weights hanging down, in front of your upper thighs. The handles should be parallel to the floor and the ends almost touching. Slowly raise the dumbbells up to shoulder height. You should feel it in your shoulders and neck. Another great exercise for office slaves.
Carpet works superbly.
Using the muscles in the small of your back, arch your upper body AND your legs off the floor. Hold for a second or two then relax. Repeating this only 8-10 times is usually enough. I throw these in just because we're already on the floor and, what the heck. Do them anyway you want.