I have this very same problem. I can sing, but I don't lead songs partly because I don't know how to adlib. If I were leading a song, when it gets to the windup, I shut up, or either say the same thing, using the same run or melody over and over again. Thanks for the advice everyone gave. To the original poster. I want to start leading songs, so I've started to practice in the car. I'll turn on a song that's basically made by its adlibs, and not listen to the person leading the song but instead just sing it as if I were singing it in church on Sunday morning, and guess what? Sometimes it actually comes out good. Now all I have to do is get over the anxiety and fear of being front and center. Hope that helps.