Going on a full-time LDS mission and doing missionary work are not one and the same.
The first is an example of the second, assuming the full-time missionary is actually doing what they’re supposed to do.
But the second, doing missionary work, is much broader and encompasses our whole lives as Church members. So, ANY faithful Church member should be able to give advice on being an effective missionary, because we ALL should have experience doing missionary work.
The young people of the Church should prepare to go on full-time missions, but more importantly, they should learn to serve as missionaries every day, regardless of whether they have the name tag and the full time calling.
If you want to help people become good full time missionaries, it’s definitely good to look for advice from people who have been (good) full time missionaries. But, since the essence of full-time missionary work is missionary work, all Church members could potentially have advice that’s just as valuable.
Everybody, but maybe especially the young people of the Church, should understand what “missionary work” really means. It means sharing the Gospel by word and example, and that’s something that not only every member of the Church can do, but every member is required to do by covenant. We will stand as witnesses of God at all times and all places. There is no asterisk saying that only when you are serving a “full time mission” do you obey those covenants. “I have never been on a full-time mission” does not mean “I have not been a missionary” or “I don’t know what being a missionary is really like.”
Everybody has the duty to be a missionary on an ongoing basis – to share the gospel with others,
When people say, “Wow, those kids will be great missionaries because their mom went on a full-time mission” … What if she didn’t? That somehow means she won’t know as well how to prepare her kids to go? Just by sharing the Gospel, she will know, just as if she had served in that particular way, because the core activity of the two things is the same.
The Primary kids sing, “I want to be a missionary now, I don’t want to wait until I’m grown …”, and while it is important to get them excited from a young age about the possibility of serving a full-time mission, we should also teach them that they don’t have to wait, and indeed shouldn’t wait, “until they are grown” to be a missionary.
A young woman, for example, should think of herself as an actual missionary, not just a potential missionary. That way when she needs to decide whether to serve a full time mission, she will already see herself as an accomplished missionary. And when she looks for a husband, she looks for a man who loves to share the Gospel, not just one who served a full-time mission. And when she is a mother someday she will always be able to say in her heart, “I am an experienced missionary and I know how to be a good missionary and so I can teach my children how to be good missionaries”. That way doing missionary work on a daily basis will always feel like a critical part of her life, regardless of whether she ends up having the opportunity to do it on a full time basis with no distractions for 18 months.
Missionary work is missionary work no matter who is doing it and for how long. So any member of the church who has done missionary work knows something about missionary work.
“It becometh every man who hath been warned to warn his neighbor.” – D&C 88:81