It’s both easier and harder than you think, but here a few points to make it constructive.

Wait ’til your asked

Sure, you can always offer unsolicited feedback, but by waiting until you’re asked gives you the advantage of knowing what they want and that they are ready to receive it. Someone who hasn’t asked for feedback is probably not ready to hear it.

If, for some reason, you feel compelled to offer unsolicited feedback, make sure that you’re doing it for their benefit and not yours.

Understand the context

Even if you’ve been asked, understand whether someone is asking for feedback or affirmation. I tend to ask this directly, which comes of as abrupt–especially when many people don’t know for sure. A smoother way is to gains some context by asking more about the project to understand their motivations for asking.

Providing a critique when someone is seeking affirmation stings, no matter how kind and constructively you are. At the same time, an affirmation seems shallow when someone is seeking constructive criticism.

Know the goal

“What do you think?” is a common way to ask for feedback. If someone asks you this, ask them to be more specific. To give effective feedback, it helps to know how they plan to use it and how much they can change as a result. The best feedback is something that can be applied.

Be constructive and specific

If you see something that you think could be improved, be specific. It takes more time to consider and articulate, but is much more informative than vague observations and opinions.

Cite your sources

If your feedback is based on research, such as recent customer feedback, survey data, or some other research, cite it! Maybe you read or learned something the presenter hasn’t (or vice versa!).

Feelings come from you

Sometimes, you’ll see something that you can’t articulate. There are two options to take, in that case.

1. You can wait until you figure it out.
   Sometimes it just takes time to bring your thoughts and feelings together into a coherent sentence. In that case, wait.
2. Other times expressing how you feel is the whole point of the exercise, but speak for yourself. Unless you’ve surveyed the audience, don’t speak for them. “This makes me feel good.” or “I like how you’ve combined the text with the image.” are perfectly fine. “It looks annoying.” really means that you find it annoying, which might bear pursuing, but it is framed in the sense of “everyone will find it annoying,” which is not the case (unless, you have some research on the subject, in which case, see the previous point on sources).

If done right, providing feedback and criticism can be a win-win interaction.