If you see someone do it well (the word ‘genteel’ comes to mind) you can find that verbos it and awkwardness will detract from both the directness and honesty.

‘Traditional’ etiquette books are actually pretty good at this stuff: one definition of etiquette is to never out another ill at ease or uncomfortable. Discomfort is contagious especially through body language, so the first thing you must do is be comfortable yourself with the feedback you’re giving.