When I asked this question, some of the best advice i was given was to be a good example, and to try to bring these truths up in a non confrontatinal or accusatory manner. Like, talk about it in conversation, rather than saying, you know what you’re doing is a sin, right?
With me, being young, I have friends who often lead lives in a way I don’t agree with, including contraception. When a couple of my friends wanted to buy a box of condoms anbd blow them up as a joke, I just smiled and shook my head, and said, "No thanks, my faith teaches that we shouldn’t’ use contraception,or be sterilized, use condoms,.etc, and I want to be shown living that! Why don’t we put little messages inside balloons instead?
We are culpable for the sins of others when we say nothing and HAD A PLACE to say something. There ARE occasions where it isn’t appropriate for you to step in- YET! someone who isn’t very close to you, for example,or a casual friend, speaking up may not be the riht thing to do yet.
As for loved ones who aren’t Catholic, try not to focus on correcting ONE sin, especially if their faiths do not aknowledge it as a sin. Instead, work on showing them Catholicism first!