To make one's bones is an American English idiom meaning to take actions to establish achievement, status, or respect. It stems from, and is a corruption of, the idiom "establish one's bona fides".
Although the idiom appears to have originated in the United States criminal underworld it has since migrated to more popular and less sinister usage; including law enforcement, legal, and religious discussions.
In popular culture
The idiom was popularized in the 1969 book The Godfather and its 1972 movie adaptation, for instance when Sonny says "I 'made my bones' when I was nineteen, the last time the family had a war", and when Moe Greene says "I'm Moe Greene! I made my bones when you were going out with cheerleaders!" The term was also used in The Sopranos several times. As in these examples, in organized crime usage the phrase refers to establishing one's credibility by killing someone.