I remember hearing this acronym in school as we were preparing to deliver our first sermons. Over and over the professor would repeat himself to us "Keep it simple stupid." Well, the last "S" for "stupid" I didn't need to hear. But the main point of the professor was that when we are preparing and preaching our sermons, we say it so that even the children could understand, or the uneducated. If the children get it, the others will too.
Dr. Martyn Lloyd Jones quotes Martin Luther as saying "When I preach I regard not the doctors or magistrates..., no, I have all my eyes on the servant maids and the children. And if the learned men are not pleased with what they hear, well, the door is open." Dr. Martyn Lloyd Jones then adds that if the learned man feels that he is not getting anything out of it, it is because he is not spiritually minded. He is not able to receive spiritual truth because he is puffed up. The same must be true when sharing the gospel. K.I.S.S. "Keep it simple, son."
What are you wanting to share with a person when you share the gospel? It is good news! God is passionate about saving sinful man. He even came to earth to take care of it Himself!
Always keep in mind that a child must understand what you are saying. This takes work. I have a much easier time explaining "justification" and "sanctification" to adults than children. But it must be broken down to it's most basic sense, so that even the uneducated can receive it. If the gospel, and all of God's truth can not be broken down for the average man, then it is an elitist message, one for only the learned, and if that is true, then it is a message that is arrogant, and to be despised.
What is the most important need to understand God's truth? Men, and children must have the accompaniment of the Holy Spirit. One may not be able to read, or write, but if he has heard the truth of the gospel, and has truly been born again by the glorious message of the gospel of God's grace, then indeed he or she has been equipped to understand things that the wise and learned cannot.
Yes, remember the acronym K.I.S.S. or even K.I.S.S.D. "Keep it simple son, daughter". BUT MAKE SURE THAT YOU ARE TELLING THE TRUTH! THE TRUE GOSPEL!
"How beautiful are the feet of him who brings...", not complex arguments for the learned and highly educated, but "who brings good news".