This is a great question and hard to answer for so many people. I have adopted the definition of success promulgated in 1955 by a World War II hero by the name of Earl Nightingale. Earl was one of only 100 survivors of the attack on the USS Arizona at Pearl Harbor.
After the war he wrote a speech which he delivered before his insurance agents. That speech entitled "The Strangest Secret" contains the following definition of success, which I teach to my college age coaching clients. It is: "The progressive realization of a worthy ideal." Studied, it will reveal a tremendously simple reality and that is; it really doesn't matter what you decide you want to do, success comes by passionately sticking to a worthy goal and continually improving moment by moment.
This may not be for everyone, but for me, it works!
I believe a copy can be found on YouTube or perhaps you can Google it. It's worth the time to listen.