If you ever had to critique someone, it can be really difficult. Finding the right words is hard, especially when it comes to someone you care about. I read a really great article recently about how to deliver criticism in a way that's going to mean the most to the person on the receiving end.
Here are some helpful guidelines:
1. Understand why you're giving the criticism in the first place
2. Always put yourself in the other person's shoes
3. Make sure to direct your criticism to the present not the past
4. Remember, and most importantly, criticize the deed not the person
"He has a right to criticize, who has a heart to help” – Abraham Lincoln