A hand model usually has proportioned petite hands, no scars or veins and has clean and soft cuticles and nails. Nails are not too long and fake nails are a no. Taking care of your "parts” especially your hands, feet and legs can help to launch your modeling career.
Taking care of your skin is always important for your whole body, but your hands can get damaged quickly if you do not take care of them. Use Sunblock if you are outside and try to stay out of the sun for long periods of time.
Parts modeling is something that a girl can do for years and years and there is no height requirement but being available is defiantly needed, a full schedule will not work to be a parts model since castings are very often and anytime.
Regular manicures are important but try to stick to light colors for your nails. Moisturizing the nails and whole hand is very important and the arms, I also try to take care of my arms as well because hand modeling can also sometimes include your whole arm and wrist as well for jewelry.
You will need photos of your hands holding something, could even be a fork, wearing rings, try posing your hands as if it were for a product ad, - these are the type of shots you want to have as a hand model.
Hand modeling can be a great way to get into the modeling business and get representation, you will go on castings for great brands and get ahead as a model and make some great money.
Try the Parts Models Agency, just google it.