Question: What is the best way to quickly warm up or get acclimated to an unfamiliar piano? That is, if you have, say, five minutes to prepare, what do you play to get your muscles and ears situated so you can make best use of your lesson time? If you sit down at a piano you've never played before, or have played very little, what's the best sort of thing to play to familiarize yourself with it quickly?
Another part of this question: What if the piano is really bad (out of tune, poorly regulated, etc.) but you have to play on it anyway?
Albert's reply: Warming up the hands is different from getting used to an unfamiliar (or even familiar) piano. If I need to warm up before playing for any audience and only have a few minutes, my warmup exercises of choice are double notes. I'll do simple exercises in double thirds or play parts of, say, the Schumann Toccata slowly, raising the fingers somewhat more than usual in order to activate (i.e., warm up) the extensor muscles. I emphasize that slow, deliberate practice warms up the fingers (and mind) better than does fast practice. I also warm up with scales and recommend them to beginning- to intermediate-level pianists for warming up. More advanced pianists can use both scales and double notes.
When familiarizing yourself with a piano, its action is even more important than the sound. Thus, the responsiveness of the keys is decisive. Is the action sluggish and heavy? Or perhaps heavy yet still responsive? Light yet unresponsive? Do the keys spring back to their starting positions upon release, thus pushing the fingers up, or is their return more natural, or perhaps too slow?
Test the resistance of the individual keys. Find the slowest speed of depressing the keys at which the piano will sound. In other words, find the softest dynamic possible for the particular piano.
Repeated notes are an especially good test of a piano's action. Repeat a single note, either using fingers 3-2-1 or 4-3-2-1 of a single hand or alternating the middle finger of each hand. Your technique may or may not be up to the piano's capabilities, but if your technique and repertoire to be performed exceed the piano's ability to respond then you will have to adapt by choosing a slightly slower tempo.
Trills—rapidly alternating half or whole steps—are another test of a piano's responsiveness. Find out how fast you can play trills without blurring the sound and while still "pronouncing" every note. Play different types of trills—articulated trills in which the fingers release the keys completely, as well as trills in which the fingers "sit" in the keys. This latter type of trill is reserved for grand pianos only and will test their double escapement mechanism, which allows a piano to repeat a tone without having to release the key completely.
Play slow passages, especially chords, slowly dipping into the keys. Are you able to play very expressively on the piano? Does the action respond to nuances of dynamic balance and voicing of piano chords? A truly good, well-regulated action will seem to play itself.
As for your final question—what if the piano is out of tune or poorly regulated?—there is but one answer: The worse the piano, the better we must play!