Not just anyone:
Different breeds of cat have many different dietary and environmental needs, make sure any prospective owner is aware of these and has the ability and knowledge to take on your cat.
Inform any prospective owner of your cats needs, likes and the costs involved in looking after it, also pay attention to any questions they may ask as if they do not seem that interested in the animals health and wellbeing, they may not be the right person/people to rehome it.
Health, health, health:
If your cat is 4 months or older, consider neutering or spaying before rehoming, this can prevent unwanted roaming, spraying and reduce accidental pregnancies which can place a burden on the new owners and possibly animal rescue centres.
Please ensure you tell any prospective new owners about the cats health and medical history also.
Make sure all paperwork such as vets information, medical history etc is provided to the new owners.
No obligation viewings:
Just because a person views your cat, does not mean you have to give it to them, if you are not happy with the person in question, just say no. It shows that your cats wellbeing is the most important concern you have.