1, Learn how CC works,
2, learn what connections are required to make it work,
3 work out if your car supports it (consult ECU Specifications),
4, Find out what Wiring is available in car.
CC on post 2010 cars are controlled by the ecu and drive by wire.
There are quite a few safety systems that need to be understood in order to retrofit CC and dont forget that your car inspection centre must also approve of the setup before it can be used on public roads.