When giving feedback try to be: 

• Constructive. The purpose of giving feedback is to help someone improve, not to identify everything someone is doing wrong. “Your summary is terrible” is not an effective comment, but “I had a hard time reading your summary because of the lengthiness.” is more helpful. Focus the feedback on the action, not the person.
• Balanced. Complimenting what someone is already doing well can be very motivating. Consider beginning with a positive comment before commenting on an area for improvement.  
• Limited. Focus on a couple of priority points rather than calling out every concern.
• Specific. General comments such as “the summary you wrote doesn’t work” may not be as helpful as “I didn’t understand some of your key summary points at first, the choice to use new terms made it difficult to tie it to earlier concepts.”
• Suggestive. It’s even better to provide concrete suggestions for how to improve, e.g., “We need to be consistent, either we look at changing the terms used throughout the presentation, or use the ones used in the summary.”