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:
It is Set Expectation => Work => Feedback => Set Expectations.
You can't give feedback to somebody and she takes as a surprise. First, set expectations. Give some time, and then feedback.
Feedback to somebody consists of two parts: what and 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 a feedback once a quarter. It's a short (2-3 sentences) feedback about event that just happened. It can be positive and negative. It's formula is the following:
Recognise the fact that happened + Give your opinion.
For example, the positive one: "I've noticed that you had an short arguments with X, I liked that 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.