The introduction to John's first letter gives us a really good standard for the things we share with others, something we know and understand. John says that what he is talking about is not just something he heard from someone else or something he read somewhere but this is something he has spent time with and has experience with. If we really do not fully understand something we are better off not saying too much about it but instead we should spend some time reading and studying God's Word to get the understanding we need about that subject.
There are many people you can see on television or on the Internet who are supposed to be "experts" in some area or even say they are Bible scholars. My question has always been why are they considered an expert or an authority on the subject? What I have seen is that often people who claim to be experts in some field or even people who claim to be Bible scholars are not at all what they claim to be. Recently I read an article on the Internet by someone who claimed to be a Bible scholar and after reading their article I wondered if that person had ever read the Bible!
In Acts 4, when Peter and John were arrested for teaching people about Jesus, Peter and John said in verse 20, "For we cannot but speak the things which we have seen and heard". This is just like what John wrote later in 1 John 1:1, we need to speak about what WE have seen and heard. It is the truth from the Bible that we personally know and have experience with that we will do the best talking about.
This is why our own personal time with God and His Word are so important; if we don't know something we can't put it into action in our own life and we really can't help other people understand it. The things we do to help other people and teach other people start with and come out of our own relationship with God. Read and study the Bible for yourself; not just so you can check up on the things you hear to see if they are true but also so you have firsthand experience with biblical truth that you can then share with other people.