Active recovery

That soreness that you feel after a hard workout is actually caused by small tears in your muscles. These tears occur so that when they heal your muscles are bigger and stronger than they were previously. This is also the reason that working out the same muscle groups on subsequent days is not recommended.

That is not to say that exercise should be discourage when you are sore. It just means doing something different. Doing some easy cardio to get your heart rate elevated and promote blood flow is a great way to reduce that soreness. Moving your body gently forces the muscles to work again and that can promote increased motion around the joint. If you are feeling extra stiff spend some time stretching after your cardio. That will help to lengthen the muscles and relax those tight areas.