It is just like anything else in that you need to start with the basics and work your way up.
I do not recommend anyone try and jump straight into CNC without at least dabbling manually for a short period
You need to feel the forces at the handles and spend time setting things up to appreciate what it is you are doing. Learning the basics of when to climb cut, when to conventional cut, when to plunge cut, how you should attack certain parts and the exact reasons why. Learning how parts are made will make you immeasurably better at designing parts as well, and anyone who ends up having to make parts you designed will love you for it.
Even taking a "CNC class" will likely only give you the basic ideas.
I have learned an insane amount on the job versus what I learned in my classes, looking back all the classes really taught me were the basics, but I still recommend that is where anyone who is interested get started. You will get to the big guns eventually, just take the time to set up a good foundation and it will make you much stronger in the long run.