Lead with intent before mechanics. 'I think we're solving the wrong problem here, here's why' lands differently than fifteen line-comments about variable names attached to a fundamentally wrong design.
Mark which comments are blocking and which are taste. Reviewers conflating the two is a top reason juniors over-rotate on stylistic feedback.
And: praise the non-obvious good calls. Nobody mentions the small refactor that made the diff readable, but those are the ones worth noticing.