Dic: make it your business to do something

• Ruth made it her business to get to know the customers.
• I know it doesn't concern me, but I made it my business to call city hall because someone had to.
• Jane took it upon herself to find out exactly what had happened to the old lady. 

* * *

■ make it your business to do something: △to make a special effort to do something.

■ make it one's business to do something (= take it upon oneself to do something): △Fig. to do something on one's own even if it means interfering in something that does not directly concern one. (As opposed to minding one's own business.)

* * *

CF. business (as a matter): a situation or activity, often one that you are giving your opinion about:

• Arranging a trip abroad is a time-consuming business.
• These killings are a dreadful business.
• I make it my business (= I feel it is my particular duty) to check the monthly accounts.
• We've got some unfinished business to discuss (= We still have something important to discuss).  

...... LDOCE, McGraw-Hill Dictionary of American Idioms and Phrasal Verbs, CALD