Constructive criticism is when the critic is more concerned about the other person's benefit than furthering the critic's own convenience. However, since we can't control the state of mind of a critic, why not take every criticism constructively?
One way to do that is to not take things personally. Judge the advice as if it were given to someone else to take off some of the sting that our egos naturally feel when criticized. Would following the advice help a person with similar goals and background as you? Imagine reading the criticism in the form of a tip in a book rather than coming from a person in front of you. Is the reasoning compelling enough for you to read further?
Criticism is as much or more about the other person as it is about you. People preach what they want to learn themselves. This is projection. If there is a lot of frustration or anger in the criticism, it is an strong indication that the person doesn't know how to accept and care for the part in himself that exhibits what he is criticizing. The critic is, in effect, asking you to model the self-compassion he cannot muster for himself. If you respond defensively, you are not only saying, "I don't have that flaw in me," your defensiveness is implicitly agreeing with the critic, "Anyone who has that flaw is bad." The constructive response would be to show how you could forgive yourself and grow if you did have that issue, whether or not you initially thought you had the issue.
Whether you respond to criticism by self-improvement or modeling self-compassion, you are taking charge of adding the "constructive" to constructive criticism and not leaving it up to the critic or your ego's interpretation of him.