When you teach via the spirit of truth, you will always learn something new:
17 Verily I say unto you, he that is ordained of me and sent forth to preach the word of truth by the Comforter, in the Spirit of truth, doth he preach it by the Spirit of truth or some other way?
18 And if it be by some other way it is not of God.
19 And again, he that receiveth the word of truth, doth he receive it by the Spirit of truth or some other way?
20 If it be some other way it is not of God.
21 Therefore, why is it that ye cannot understand and know, that he that receiveth the word by the Spirit of truth receiveth it as it is preached by the Spirit of truth?
22 Wherefore, he that preacheth and he that receiveth, understand one another, and both are edified and rejoice together.
23 And that which doth not edify is not of God, and is darkness. (D&C 50)
For this and other reasons, you should always be prepared to learn something, even while and perhaps especially while in the act of teaching others.
The first key in teaching others is to remember that everything you know is incorrect or incomplete. Every time you seek to teach another, realize that they might actually teach you. A teacher must be exceedingly meek to discern and to learn a lesson from the pupil. A tremendous test of meekness is the attitude one has when interacting with those they assume know less than them.
The prideful assume that any precept that conflicts with their current understanding must be false. They judge truth based on what they already know rather than objectively evaluating it.
The meek, on the other hand, recognize that anyone can teach them something. They assume anything said might be true, and are open to the possibility that they may be wrong. Their current knowledge paradigm is always on the altar.
God said, “All truth is independent in that sphere in which God has placed it.” (D&C 93:30) Two people can testify of competing truths and both be right, because truth is contextual on awareness, and everyone’s awareness is different. The Spirit can reveal something that is true in your “sphere” of understanding, but to someone who has attained to a different “sphere,” or a higher degree of knowledge, it would be false.
This concept is hard for some to accept, but consider a decimal point number as an analogy. Additional digits of precision are true, as are fewer digits of precision. However, to the engineer possessing ten digits’ precision, the decimal of two digits’ precision is less true, and for some applications, downright wrong. Just as one could add digits of precision infinitely, God’s truth never ceases.
Because the degree of glory we enjoy in life is dictated by the degree of God's law that we live, we should always be willing and eager to receive further light and truth in order to expand and clarify the law we currently have. This will likely cause us to change what we are doing. To facilitate this process, we should always be willing to ask questions to further our understanding of answers we have already received—like a child.
We should never judge someone who sincerely and fully believes that their actions are in accordance with God’s word when we have received a different answer to the same question, knowing that it is very possible that they have progressed past us in knowledge. Instead, we should do as Nephi did when presented with his father’s strange claims of having a vision that contradicted Nephi’s understanding: we should pray and ask God. Even if we are not prepared for the answer, God will mobilize the necessary experiences in our life to bring us to the point where we can receive the same knowledge.