To master or acquire a skill or habit so that it becomes second nature; to become accustomed to something.
毎日英語を聞いていると、リスニング力が徐々に身につく。
If you listen to English every day, your listening ability will gradually become established.
新入社員はまずビジネスマナーを身につける必要がある。
New employees first need to acquire business manners.
毎日の反復練習が習慣となり、やがて身につくでしょう。
Daily repetitive practice will become a habit and eventually stick.
彼女は日本で暮らして、自然に日本語の表現が身についた。
She lived in Japan and naturally acquired Japanese expressions.
To remain with or stick to someone; used in contexts like 'ill-gotten gains won't stick' (retention/keeping).
悪銭身に付かず、結局得た金はすぐなくなった。
Ill-gotten gains don't last; in the end the money he got was soon gone.
経験として身についた知識は簡単には忘れない。
Knowledge internalized as experience is not easily forgotten.