Giving and receiving feedback is an artform few have mastered and we all could practice getting better at.
Most of us have heard that we should "start with something positive." This assumes that most feedback is negative and we have to resort to sugar-coating it as though administering medicine to a child. All feedback should be positive, in that it should be constructive. Instead of "something positive," start with a shared goal, something both the giver and recipient want to achieve — it could be as specific as publishing a piece of writing or as general as being more productive in one's day — then provide information that will help you accomplish it together. Focusing on the goal rather the person has the added bonus of avoiding the pitfall of giving inappropriately personal feedback.
Being honest doesn't mean being confrontational. In fact, a person who feels defensive is a person who is temporarily unreceptive. This is what most people think of as honest: "I don't like that thing you did there." But this communicates the same thing and is honest, "I appreciate what you were trying to do, but next time could you try it this way?"
A response is more valuable than a reaction. Last year I worked with a company whose CEO would leave comments in Google Docs like, "meh" or "who cares?" If he'd taken the time to respond thoughtfully about why he was reacting this way, I would have at least been able to try to fix it. Instead, he wasted a lot of money paying me to guess.
Think of feedback as a traffic or weather report or map that you use to determine the best route home.
If feedback requires special training or instructions, then it isn't clear. You can tell me I'm a 3.5 and explain it up and down, but it still won't be terribly meaningful to me. I know large businesses in particular are challenged to ensure that the feedback that's being given is equal across the board, but I still think a human conversation trumps a number, chart, or letter grade any day.
When giving or receiving feedback, imagine it as a wonderful gift. This will make you so much more generous and thoughtful in the feedback you gift, and help you find something of value out of even the worst. Once as part of my annual review I was told that I should "smile more than meetings." This remark was a gift in that it helped me decide to go work somewhere else.
Not sure where to begin?
Invite someone to give feedback to themselves: What do you think is working well? What still needs work?
Provide context: Here's something you may not have known that you should think about!
Offer to help: What's the best way for me to help you right now?