Welcome to CAF! And what a great question.
The answer to your title, “How do you save others???”, is to let God do it. We cannot. But we can be His instruments, and I’m sure that is what you meant.
Keep praying. That is essential.
As to how to broach the subject of conversion with them, here are a few scattered ideas.
First of all, you have to have a relationship of trust with them before you “earn” the right to be heard. When I made Cursillo (a weekend “course” in Christianity, which I highly recommend), we learned that you have to “Make a friend, be a friend, bring a friend to Jesus.” IN THAT ORDER.
Actions speak louder than words. If they know you are Catholic/Christian, and they see the fruits in the way you live, in charity, kindness, service to others, they will want what you have. Saint Francis of Assisi said, “Preach the Gospel at all times and when necessary use words.”
If your friends are baptized Catholics but in need of deeper conversion, perhaps the greatest good you can do for them is to bring them to the Sacrament of Confession. Like the people in the Gospel who brought the sick man to Jesus and lowered him on a pallet through the roof. (You will probably have to use a different technique! :D) Perhaps by casually mentioning how you have benefited from it, the peace it brings you. Or just inviting them to come along when you were planning to go. It’s kind of delicate, knowing the best way to invite without appearing to judge or accuse them.
Always pray for the guidance of the Holy Spirit in your apostolate. Sometimes I have prayed, “Holy Spirit, if you want me to speak to this person on Your behalf, give me an obvious opportunity, and give me the words that will work best,” or something along those lines. I have been amazed at the ways the Holy Spirit has responded to this type of request!
You can also pray to your friend’s guardian angel. Their angel desires their conversion even more than you do.
There are probably lots of other ideas out there. The book Search and Rescue: How to Bring Your Family and Friends Into, or Back Into, the Catholic Church by Patrick Madrid and Scott Hahn may help. amazon.com/Search-Rescue-Family-Friends-Catholic/dp/192883227X/ref=sr_1_3?ie=UTF8&s=books&qid=1237329979&sr=1-3
God bless you for your concern, and may your efforts be fruitful.