I've confronted someone, seriously, on at least two different occasions. On one of those occasions, I definitely could have done it better, but I still went into it with the right heart and intentions. It might be good to set up a time to meet, so they aren't taken off guard.
Indeed, be very prayerful about it. Make sure that you are not being accusatory, but rather make your intention clear that you are there because you want to know more, or because you are genuinely concerned about them or a situation.
Criticism and confrontation are hard to take. They may be very upset at first and get defensive. Be prepared for that. Continue to be patient.