To be a spiritually mature missionary you should know and understand and implement the following
Power of the Holy Ghost and Gift of the Holy Ghost
Prayer of Faith, applied to both teaching and finding
Identifying the Spirit
Personal Revelation
Edification
Language of the Spirit
Language of the Spirit
President Thomas S. Monson taught:”There is one language...that is common to each of missionary – the language of the Spirit. It is not learned from textbooks written by men of letters, nor is it acquired through reading and memorization. The language of the Spirit comes to him who seeks with all his heart to know God and keep His divine commandments. Proficiency in this language permits one to breach barriers, overcome obstacles, and touch the human heart.” (PMG p.133)
Elder Jeffery R. Holland taught: “More important than speaking is listening. These people are not lifeless objects disguised as a baptismal statistic. They are children of God, our brothers and sisters, and they need what we have. Be genuine. Reach out sincerely. Ask these friends what matters most to them. What do they cherish, and what do they hold dear? And then listen. If the setting is right, you might ask what their fears are, what they yearn for, or what they feel is missing in their lives. I promise you that something in what they say will always highlight a truth of the gospel about which you can bear testimony and about which you can then offer more....If we listen with love, we won't need to wonder what to say. It will be given to us- by the Spirit and by our friends” (PMG p.185)
“Learn to ask questions as prompted by the Spirit. The right type of question at the right time can greatly help those you teach to learn the gospel and feel the Spirit. Asking the appropriate questions at the right time requires that you are in tune with the Spirit, that you listen to those you are teaching, and that you focus throughout the teaching experience. Effective teaching can be hard work and requires concentration and effort on the part of you and your companion.” (PMG p.184)
Finally another emphasis on commitments
Elder M. Russell Ballard spoke of the power of the Spirit:”True conversion comes through the power of the Spirit. When the Spirit touches the heart, hearts are changed. When individuals...feel the Spirit working with them, or when they see the evidence of the Lord's love and mercy in their lives, they are edified and strengthened spiritually and their faith in Him increases. These experience with the Spirit follow naturally when a person is willing to experiment upon the word. This is how we come to feel the gospel is true.” (PMG p.93)