The two parts of effective validation are: identifying an emotion and offering some type of justification for that emotion.

An example: When someone is telling you about a frustrating situation you might respond with, “Oh, I would be just as frustrated!”

This shows you are feeling (or would feel) the same frustration that the speaker is feeling (justification), and they’re able to say, “Oh, he feels it too,” which is validating the speaker’s feelings.

If someone is excited, and you act exited along with them, that justifies how they are feeling.

Source: The Art of Charm episode 721 with Michael Sorensen