Challenging opinions

For me, the things I find most difficult about challengin the opinions of other people is to find the correct manner and way to tell them my opinion. I do not want them to missunderstood what I want to say or feel I am attaking them.
I deal with these by thinking about some appropiate words at the time of challengin someelse opinions and giving valid reasons and evidence in order for them feel intersted and take the time of think a little bit about it.