My approach to preparing a sermon has been that I must never assume I will ever get to preach again. That’s a bit of a cop-out, though. It ignores the fact that we must always seek to improve, and that also means accepting that this next time mustn’t be our last or best attempt at faithfully digging out first century questions and bravely essaying twenty-first century answers.
In any case, thinking in such a linear fashion — this time, next time, the time after that — won’t be too helpful if you don’t have the luxury of being a full-time student and your deadlines are as fixed as the passage of days.
All that preamble is to preface this bit of ‘preaching lore’ I came across — hope it helps my fellow hatchlings:
How Much Advance Planning Should We Do for Our Sermons?
Preachers vary widely in their planning habits. Some preachers have well-organised minds, and with the aid of a calendar and a lectionary they plan their preaching months in advance. A few even take a week or so of study leave to sketch out a general preaching scheme for the coming year. Most of us are less disciplined, beginning the next sermon only after the present one has been delivered.
The best wisdom is that every preacher can be actively at work on five or six sermons at once. A good method is to create separate file folders for, say, the next half-dozen sermons. The biblical texts should be chosen and enough of the exegetical work done on these texts to know the general direction of each of the sermons. The preacher can then browse through these files periodically to keep the upcoming sermon themes in mind. Clippings from the newspaper, quotes from novels, pastoral experiences, and other ideas can then be placed into the files so that, when the time comes to create a sermon, its folder will already contain some working material. As soon as a sermon is complete, a new file is made to take its place at the end of the line. Older homileticians called this method a “homiletical garden”. The big task is in setting up the system, since exegetical work on several sermons is required. Once the garden is planted, however, it can be tilled and cultivated as a matter of routine.
— The Witness of Preaching (2nd ed.) by Thomas G. Long (Louisville, Kentucky: Westminster John Knox Press, 2005), pp. 234–235.