I think it’s important that people closely examine their motivations for telling other people what to do. If one is feeling superior or better than the person he is considering remonstrating with, this will come through in the tochacha & it will almost certainly not be well received. Also one should try to put himself in the other’s place & consider how he’d feel if he were on the receiving end. If he would feel offended, he probably shouldn’t give that tochacha.
I understand that doing this requires a lot of self-awareness & empathy, but I think it’s essential.