Writing about the act of leading prayer in corporate worship, Hughes Oliphant Old commends the practice of praying on behalf of others that is spontaneous, but notes that spontaneity does not equal a lack of preparation.
A significant aspect of that preparation is the past and ongoing personal prayer life of the one leading in prayer, actions which involve an intimate experience with the content of Scripture and a rich prayer life outside of corporate worship.
He makes a very helpful point that the spontaneity of true prayer which is desirable is the fruit of what he terms as a ‘profound experience’ of past prayers.
…the spontaneous prayer that one often hears in public worship is an embarrassment to the tradition. It all too often lacks content. It may be sincere, but sometimes it is not very profound. One notices sometimes that the approach to prayer that these prayers reveal is immature, if not simply misleading. Spontaneity needs to be balanced by careful preparation and forethought. It needs to be supported by an intense payer life on the part of the minister. One must be well experienced in prayer to lead in prayer. One can hardly lead if one does not know the way oneself. Spontaneity has to arise from a profound experience of prayer.
Hughes Oliphant Old, Leading In Prayer, Wm. B. Eerdmans Publishing Co, 1995, pg 5.