However, when I think of this phrase when it concerns myself that it is not about lying, it is just about saying too many words. Like the other day, I was trying to explain how baby sea turtles are born to my daughter. It isn't a difficult concept, but I would explain it and then re-explain it until my daughter had no idea what I was talking about. I thought of the phrase "put your foot in your mouth" because if I could just simplify my thoughts, she would understand.
Thankfully, God knows our hearts. You do not have to worry about "putting your foot in your mouth" when it comes to God. He will understand your convoluted explanations and He will know if you are lying. God wants us to share our hearts with Him so He can get involved, if we can't be honest with God, we will not get desirable results.
The same goes for sharing the Lord with others. When we lie and put on a facade about who we are as Christians, it does nothing to advance God's Kingdom. People don't need to see how perfect our lives are, they need to see that we are but imperfect humans relying heavily on a strong King. When we say so much that we mix-up our message or if we are not completely honest with others, we are fools.
Pray for God to give you the words to say when talking to others about Him and when to stop talking. He will press on your heart exactly what to say, or not say, in the moment to draw His children to Him.