To start with, you set the temperament, making certain that one
string of each note is up-to-pitch (A=435 Hz is okay on older pianos
built for that pitch), and the others fairly close to the chosen
pitch for equalizing string tension.  Achieving this first step will
take several tunings if the piano is "way down".  Octave stretching
is done in the usual manner to avoid a flat treble.

Then the fun begins.  With one string of each unison in perfect
tune, the second string is tuned very close to produce slow beats,
and in the 3-string unisons, the third string is tuned to produce
several beats per second, perhaps bordering on the discordant to
the classically trained ear.  (What you do not want is a piano that
sounds like one with loose pins that hasn't seen a tuning hammer in
30 or so years!)

The degree of out-of-tuneness should focus on the low to middle
treble and taper off in both directions, the single-string notes
of course being in perfect tune, and likewise the extreme treble
unisons.  I avoid being too specific, because the tuner needs to
"get the feel" of a particular instrument's tonality.

The condition of the piano's hammers is of utmost importance.
Forget about the shellac, thumbtacks or installing a mandolin rail!
Hopefully the hammers are original, fairly hard and long-wearing,
having had little or preferably no resurfacing.  Resurfacing is then
done in the following manner, always by hand.

With a sandpaper file, remove only the felt between and beside the
string impressions.  Do not file below the bottom of the string
impressions.  Traces of them should remain.  You will be then left with
a flat, not rounded, striking surface.  This does not hurt the hammers
in any way, because the usual shaping and voicing can always be done
later, if one desires to de-honky-tonk the instrument.  Likewise with
the tuning.

I've seen and heard a lot of YouTube player piano videos, and here is
what I consider to be just about the best.  Who says a piano has to be
out-of-tune to sound this good?  Obviously, selection of the roll is
a key factor here:  http://www.youtube.com/watch?v=mUd-h4rt7xc 

Jeffrey R. Wood

 [ Compare with http://www.youtube.com/watch?v=cYlDkVSVcdU&NR=1 
 [ -- Robbie