get on (one's) good side
To obtain one's good favor. How can I get on the boss's good side when he's so fickle? If you want to get on my mom's good side, I suggest getting a bit dressed up for dinner.
get on (someone's) good side
To become the object of someone's favor; to do something that causes someone to be pleased. The superintendent is a powerful woman in the school district, so be sure to get on her good side. I'm hoping to get on John's good side with this cake I baked for him.
get on someone's good side
Win someone's approval or support, as in Kate offered to walk the dog in order to get on her aunt's good side. [c. 1930] Also see in good with.