How can you approach someone in a manner where you tell someone that what they're doing is wrong without upsetting them or hurting their feelings?

Sometimes when one thinks something is wrong or does not agree with someone else does not mean it is. Sit and speak with this person and instead of "telling them they are wrong" suggest a different way of doing things or explain the outcome of their actions as to show them it is possibly not beneficial for them to be doing it the way they are.