Which early canonical references help one find a skillful teacher?

There is a similar question from the *Vajrayāna* stand-point in which I gave an answer that was partially off-topic since it wasn't from that tradition's texts. So I thought it could be useful for newcomers to know what the early texts say on this matter. *Note: Since one is explicitly encouraged to answer his own questions for the sake of sharing his knowledge, I've also answered the question below.*