Even having the best CCTV camera surveillance system is ineffective if the video quality is distorted due to a dirty security camera lens. Every CCTV camera should be cleaned at least on a monthly basis for good quality footage. All you need is a clean microfibre cloth, and lens cleaner solution (optional).
First and foremost, you need to switch off the CCTV camera so that there is no damage to the device. Remember, never clean a camera while it is switched on as it may be unsafe for the person performing the cleaning.
Next you can use an air blower or vacuum cleaner to blow off the loose dust. This reduces the chances of scratches on your lens. Alternatively, you could simply blow air over it using your mouth.
And then, add a little lens cleaner solution to your clean microfibre cloth and wipe the lens. Do the gently. A cheap alternative to lens cleaner solution is to open your mouth and exhale over the lens, then use the moisture from your breath to clean the lens.