I found this on here some time ago and use it for carbonating my kegs. No issues so far and seems to work very well. Hope this helps.
1. After the fermentation process is complete, clean and sanitize you corny keg.
2. Siphon the fermented wort into your Cornelius keg and install the cap. Try to keep any contaminates out of the finished wort. Some beers may need to be lagered before the charging of the corny keg takes place. Check your recipe for this step.
3. Take a screw driver and set the low pressure gage to about 30 psi. Turn the gas out valve on the regulator to the off position. Connect the pin lock or ball lock fitting to the proper valve on the Cornelius keg.
4. Turn the valve quickly to the on position. This will help seal the cap to the corny keg. Check the valve stems and cap for any possible leaks with a soapy water solution or glass cleaner. Look for bubbles to appear around these places especially around the cap.
5. If you see any bubbles remove the gas line to the Cornelius keg and drain the pressure in the keg by pushing down on the center of the gas (IN) stem with a small screw driver or a pocket knife to relieve the pressure. Adjust the cap by breaking it loose with the palm of your hand or a rubber mallet. Re-center the cap. At the same time pull up on the cap while locking it in place with the safety locking bar. Repeat step 4 after you reseal the cap on the Cornelius keg.
6. After the cap is sealed leave the pressure on @ 30 psi. Sit down in a chair, lay the keg across your knees and rock it back and forth for about 5 - 7 minutes. This will help the Co2 to absorb into the beer at fast rate by creating more surface area for the Co2 to come in contact with.
7. Now its time to put it in the refrigerator and let the Co2 super saturate the beer. You might think that’s it, but there is still a little more to it. After about a week, hook the gas back up to the corny keg for about 3 - 4 days @ 10 psi. This will complete the saturation of the beer.
8. While in storage leave the Co2 attached to the Cornelius keg. This will insure your beer will always be ready to drink. Before serving remove the Co2 hose from the keg. Bleed off the pressure as in step 5. Reset the pressure on the regulator to between 3 & 5 psi. This will allow you to have nicely carbonated beer without a lot of foam.
*** I forget who actually wrote the instructions from here, and can't seem to find the post at the moment, but thanks go out to the original poster.