Why do we give feedback? To help somebody to become better at something, e.g. their professional job, communication, etc.
Feedback is just a part of the bigger process:
Set Expectation => Work => Feedback => Set Expectations
You can't give feedback to somebody and she takes it as a surprise. First, set expectations. Give some time, and then provide feedback.
Feedback to somebody consists of two parts: 1) what and 2) how. What has (not) been done, and how it was (not) done.
Feedback can be positive and negative. The more positive feedback, the better. And then negative sometimes.
"Standing feedback" almost in real-time (right after when something happened) is way more effective than feedback once a quarter. It's a short (2-3 sentences) feedback about an event that just happened. It can be positive or negative. Its formula is the following:
Recognize the fact that happened + Give your opinion.
For example, the positive one: "I've noticed that you had a short argument with X, I liked the way you handled it with concrete examples". It should be exact.
Feedback should be regular.
Review feedback requires preparation.
1. Focus - what's the main message that person should understand.
2. Examples (2-3)
3. Possible solutions
P.S. Want to learn more, see the talk of Dan North - Making a Sandwich Effective Feedback Techniques.