Sometimes I'll begin the work by doing a harmonic analysis of the thing. That's fun to do on the train, and gives me the opportunity to flub the inner two voices while hanging on to the bass and melody. Unitarians are notoriously bad singers, so not only do the same hymns we know get repeated time and time again, but as long as you have the melody and basic predominant-dominant-tonic structure, you'll be fine.
For practicing: I go by systems, maybe half systems. Start with hands alone briefly (maybe 5 minutes total) and move on to half or quarter systems or pushing them together. It's a kind of memorization for me, a convincing of each finger that the next motion on the page is the only possible following motion. Playing the right sequence, then, just feels like home, stability, and complicity. And move along, practicing my half or quarter systems plus a chord or two of the next, so when I later graft them all together it feels more natural. A common pitfall is to make the chunk too long, or keep playing a part I know well; good practicing means constantly challenging my comfort with the piece. I can't even think of halting until l I can play it through a few times in a row perfectly. And then I let it sit in my head for a bit while I begin the other hymn.
Returning to the first (and later the second) him, I do run throughs and take care of problem spots, often in quarter-system chunks. I try also to play it through as if performing (i.e. through each of the voices); it's then a matter of hanging onto your continuity, keeping your mind from wandering, and relaxing into the soft crevasses of a piece.
By this point I conk out and wake up, and do a remedial practice. At a certain point there's only so much work I can do. I play without looking at my hands, and the key size and action on the sanctuary's grand is much different than my upright's. I try to arrive around 9:30, make pleasantries, and bang things out.
In addition to the two hymns I'm asked to play a prelude, offeratory, and postlude. These are very short, and end up being snippets of pop songs, or most often sections of things I've already written. I sometimes debut things there, taking the postlude to perform something for longer. If I'm working on a classical piece I'll play a section, but that's always less fun than getting comments on that "interesting thing you just played." And the hymns? They'll fly or they won't, and if the sextant's there he'll probably get very critical, and he can go away.
Pit falls: twice I have had even a small amount of alcohol before attempting this. Both times have been terrrrrrible.
