As simsaladimbamba stated CCC is a great program that not only backs up your internal drive but can clone it as well. It allows for scheduling and can be used for booting too in case of internal drive failure. I use this with one of my external drives.
With my other external backup drive, I use Time Machine with
iScheduleTimeMachine app. iScheduleTimeMachine allows for more flexibility in scheduling Time Machine and when I want backups to occur.
All suggested are good apps that will work for you. It is up to you which one has the features you like the most.