The "wiper" is the seal that keeps dust and grit out of the inside of your shock. Its job is to wipe away dirt as the stanchion telescopes into the slider. To perform its job properly, it just be moist with lubricant. When dry, it will hold the dirt against the stanchion and grind away the finish! The wiper should be cleaned and lubed about every 25 hours of riding. (If you ride one short trail weekly, this means once per season. If you're a hard-core long-and-dusty trail rider, this could be once a week.)
First clean the stanchion tubes. Check for dings and scratches. If there are any rough spots, buff them smooth with steel wool.
Now rub a very thin coating of shock lube (example Slick Honey or Red Rum) on the stanchions.
Using a very thin screwdriver, CAREFULLY pry the wiper out of the top of the slider a tiny bit. Be gentle -- you can easily gouge the soft metal of the slider tube or damage the wiper itself.
Now lube the ring. Use a thick oil, such as Red Rum, Slick Honey, or Tenacious Oil.