Prioritize the information you discuss. Don't discuss every detail, because that can overwhelm and frustrate a tutee more than it can help. Focus on key concepts and help the tutee work through those. 

Try bouncing questions back to the tutee. Occasionally, it is OK to answer direct questions, but more often, try to encourage tutees to work through ideas and come up with their own answers. (e.g.: "What do you think?") 

Focus on sharing ideas and information, rather than giving advice. Feedback tends to be more effective when it is two-way. Encourage discussion. Both praise and constructive criticism should be included. If feedback is always negative, then motivation will be low. (e.g. "I know when I write, I often get frustrated with introductions because there are so many ways to start. What frustrates you about this intro?")

Research has shown that regular and continuous feedback is a major factor in enhancing performance and motivation because it enables individuals to judge more clearly how they are performing against their objectives/targets and other expectations. 

Encourage self-criticism. People are more willing to accept criticism when they have recognized their own strengths and weaknesses. Start by encouraging them to appraise themselves and then build on their own insights. (e.g. "What do you feel gives you the most trouble with writing? Where do you feel that algebra loses you?")

Be helpful rather than critical. Negative feedback can destroy confidence and motivation. Balance out and keep a sense of perspective. (e.g. "I really like your attention to description in this paragraph. It draws me in as the reader. Are there other places you could add more of this descriptive detail?")

Suspend judgment. Try not to put your own thoughts in until you take your time and make some mental notes to check out later. 

Let them finish. Don't jump in, wait for the tutee to finish talking and you have a full picture. 

Avoid arguing, denying, justifying or minimizing. It's their point of view; decide what you want to do with the information.