After the initial cleaning using water or any other detergent, it is important to wipe off the cleaning agent from the surface of the DVD, CD or Blu-ray using a dry cloth; if it is still not as clean, repeat the process again until the grease, fingerprints or any other smudges are removed. Make sure you repeat the cleaning in the same motion as described above.
Once you are satisfied that the disc is clean, let it dry completely before attempting to play it, or place it inside any electronic equipment. Playing a wet CD, DVD or Blu-Ray will damage the machine and the disc.
It is also advisable to routinely clean the internals of your equipment used to play the discs, as this can also contribute to the dirt on a disc, due to years or months of accumulated dust within the machine.
Ideally, discs should be looked after from the start to avoid emergency cleaning, and the best way to store discs is in their original casing, or a multi-pocket CD wallet. Well maintained discs will last for a long time and will need very little cleaning.
If you have a large collection of discs that require cleaning then it is advisable to invest in a disc cleaning kit which will have a selection of cleaning cloths and liquid solutions.