If you have a bathing platform or boarding ladder and the person in the water is able to help themselves, use it if it safe to do so. If they are unconscious or exhausted, a form of lifting gear will need to be improvised. A short strop used in conjunction with a block and tackle rigged on the end of a halyard would make it easier for a heavy casualty to be brought on board. A parbuckle can be improvised by using ropes, nets or a small sail, and the rolling the person out of the water. A dingy provides another option for recovery, perhaps by partially deflating on section of the sponson tube to make it easier to get them on board.
Prevention is better than cure.
Ensure that all actions and safety precautions to prevent a person overboard have been taken and practise drills regularly in all weathers and sea conditions - You could save someone's life. How to attract attention in an emergency. A VHF radio, which can be portable, will enable you to summon help by calling the Coastguard on channel 16. If you use a radio you need to obtain an operator's certificate and an annual licence. Call the RYA for details.