Most Christians probably learn how to pray from participation in corporate worship. In the Catholic tradition (Roman Catholic, Orthodox, Anglican/Episcopal) this would mean that the faithful are instructed by the prayers of the traditional liturgies. To some extent the same is true in the mainline Protestant churches, although the latter rely more on contemporary prayers.
In the free church tradition, however, instruction in prayer will depend on the individual called on to offer prayer spontaneously. In practice, spontaneous prayers often turn out to be rotely repeated prayers of very poor quality. Consequently, their value in teaching people how to pray is limited if not negative.
–Hinson, E. Glenn. “Private Springs of Public Worship.” Review and Expositor (1983): 109-117.