How can you improve your singing voice without any lessons or singing programs?

The short answer: You cant...very much. The long answer: You can improve your voice a bit on your own to a certain extent, but not nearly the results you would see by studying with a teacher or at least by having a good set of technique exercises. Also, when your voice gets into trouble, you won't know how to fix it and it won't last for as many years as it would with good technique.