Have an idea.
This is the easiest step because anyone can have an idea. “Four young women live in Brooklyn.” “A widowed housewife sells marijuana.” “A mafia boss goes to therapy.” “I am Larry David.” Anything can be an idea!
Have someone else’s idea.
There are currently two men who have more money than every teacher combined because they said “What if we buy the IP from a fantasy writer, make THAT a show, then when left to our own devices, mess up the ending in a way that makes people physically angry for months.” This is by far the best route.