I'm recommending this classic article because it accurately describes how giving feedback is an art -- in its broadest form, it is simply communication from one human to another. This expression of performance can take many forms, and the article gives some advice on how you should express your feedback. It's well-written and has some good advice.
Ep. 84: The Power of Continuous Feedback (feat. Steffen Maier, Impraise) - Zenger Folkman