Most feedback fails in one of two directions. It is either so softened that the person walks away thinking everything is fine, or so blunt that they spend the next hour defending themselves instead of hearing you. The skill is finding the narrow path between cowardice and cruelty, and it is a skill, which means you can get better at it.
Start with the actual goal. You are not giving feedback to feel honest or to discharge your frustration. You are giving it because you want the person to do something differently and you believe they can. If that belief is not there, what you have is not feedback, it is a complaint, and you should sort out your own feelings before you book the meeting.
Be specific to the point of being almost mechanical. Telling someone they need to be more strategic is useless. They cannot act on a label. Telling them that in the last two planning meetings they jumped to solutions before the group had agreed on the problem gives them something to grab. Good feedback points at behavior, on a date, that the person can picture. Vague praise has the same flaw, by the way. People learn nothing from being told they are great.
Separate the observation from the story you have built on top of it. You saw someone go quiet in a meeting. That is the observation. The story is that they did not care, or were not prepared, or were checked out. You do not actually know that. Maybe they were sick, or had just gotten bad news, or did not want to talk over a junior colleague. Lead with the observation and ask about the story. You will be wrong about the story more often than you expect.
Give it close to the event, and in private. Feedback saved up for a quarterly review has gone stale and usually arrives as a list, which feels like an ambush. A quiet word the same day, while the moment is fresh, lands far better and costs the person far less face.
Then stop talking and let them respond. The most common mistake I see is people delivering the feedback and immediately filling the silence with reassurance, which dissolves the whole point. Say the thing, then wait. The pause is uncomfortable. Sit in it. What they say next tells you whether they heard you and whether your read was even right.
And watch your ratio over time. If the only time you pull someone aside is to correct them, they will start to flinch when they see your name in their calendar, and people who are flinching do not learn. Notice the good work out loud, specifically, often. That is not flattery. It is what makes the hard conversations survivable, because the person knows you see the whole of them and not only the misses.
The aim is never to be the smartest critic in the room. It is to be the person whose honesty someone can actually use.