Carefully!

I try to get people to critique themselves by first asking them to score themself out of ten and then ask them what they thought was good and bad about their performance.

This enables you to offer ways to improve on both the good or the bad.

This works with most people. However, you always have to be aware of those who are so bad they think they are brilliant and cannot comprehend that they need to improve!

And those who just cannot accept criticism from anyone.

It also helps if you can put yourself in their relative position.

After all I was there myself at one time and I'm still learning.

CC