Active Rest Day - Spend some time playing a sport, go for a hike, throw a Frisbee, just enjoy the beautiful weather we've been having!
Dealing with Muscle Soreness Part Two
Warm Up - Much of the stiffness and soreness can be dealt with by simply engaging in some light activity. Going through a decent warm-up will help to provide an increased fresh blood supply to recovering muscles, and performing full range movements will help to fend off stiffness. This can also be incorporated on rest days in the form of playing a sport, rock climbing, hiking, swimming, or some other light activity.
Eat Right - Eating a paleo diet (What Do I Eat?) will help improve many aspects of your body's performance. The immune system is strengthened, inflammation is reduced, skin health is improved, digestive health is improved, and RECOVERY IS IMPROVED SUBSTANTIALLY. Not only is recovery quicker, but also more effective. It will result in more performance gains more quickly(from my experience, and the thousands of cases of anecdotal evidence out there).
Fish Oil - You read it right. You eat it; please don't slather it on sore muscles(never tried it, but I wouldn't do it even if it worked like a charm). Fish oil is a concentrated source of omega-3 fatty acids, which, as discussed before, have anti-inflammatory properties by producing certain eicosanoids. Intense exercise causes microtrauma to muscles, and leads to an inflammatory response. This inflammation is needed for muscle repair and growth, but having an omega-3/omega-6 imbalance in our diet (pretty much everybody does) leads to excessive inflammation and pain.
DO NOT USE NSAIDs (ibruprofen, Tylenol, aspirin, etc) - Nonsteroidal Anti-Inflammatory Drugs can have been shown in many cases to reduce muscle growth caused by training stimuli. In other words, that training you did to get that sore, won't help you improve as much if you take NSAIDs. There are also a host of other side effects such as liver damage, increased risk of ulcers, etc, you just want to avoid NSAIDs in general.