Wrist wrests are really ergonomically dangerous.
Its better not to have one.
Ok but if won't listen to me and u insist on having one then
1. Make sure it is soft, like one of those rubbery ones. NOT HARD PLASTIC. Not wood. Not iron. Not steel.
2. Do not ever type with your wrist flat down on the wrist rest. Raise your hands up in the air while you type.
3. If you have a sideways keyboard then it is totally ok to rest your wrist on the soft rubbery wrist wrest
sideawys. By holding your wrist on the wristrest sideways you are not smashing your tendons down into your bones.
If you type correctly, with your keyboard in your lap then you won't want or need a wristrest.
> Why is it bad to type with my wrist down on the wristrest?
I'm glad u asked that

Think about what you are doing for a second.
Most of your finger muscles are halfway up your arm.
They pull and release tendons. Tendons are like pieces of string or fishing line. They are long and thin. If you bend your wrist very far or if you smash your wrist down on a wristrest then those long thing lines are dragging against the flesh and bone inside your wrist.
Your wrist bones are called Carpal bones. Ppl who use their fingers a lot, or with great weight, with bent wrist or pressure on wrist have a really good chance of stripping out their tendon sheath in the carpal bone area and causing horrible tendonitis or carpal tunnel syndrome.
Trust me, u do not want to do that.