There are always various things that can be done to improve the tone and touch of a piano. Merely tuning a piano will make a significant improvement instantly, but going a step or two further can really inspire a player.
Hammer wear can happen fairly quickly, especially with a student on a mission! The rounded hammerhead becomes cut by the constant hitting of the strings and the tip starts to become square. More felt hits the strings than normal and this causes the harmonics to change. When tuning with the hammers in this state, it will sound alright, but not as good as it can. Only about 1 centimeter of felt should contact the string. Filing the hammers becomes necessary to restore the original shape of the hammer. With a sandpaper file, felt is removed mostly from the shoulder of the hammer to bring a rounded point back to the hammer. When the set is complete, the Hammers look a lot newer in that a layer of felt has been removed. Quite often, the tone becomes brighter throughout the keyboard. Voicing the hammers may then be needed to restore a more mellow tone. A very hard hammer should be toned down to produce a clear, pleasing sound.
After filing, the hammer is slightly shorter and regulating let-off is sometimes needed. When the key is played slowly, the hammer should come to within about three millimeters of the strings before escapement occurs. The Jack has to ‘escape’ from the hammer butt or knuckle (upright or grand) before the hammer contacts the strings. If the jack can’t escape, the hammer will block against the strings and will not sound. If escapement happens too soon, power is lost from the action, and the pianist has to play harder to achieve proper forte when needed. Also, when playing pianissimo, the notes may not sound when let-off happens too early.
I find a lot of pianos, especially uprights with shorter keys, that key dip is too shallow. Both black keys and white, not going down far enough. This also causes difficulty when trying to regulate let-off. By increasing the key dip, the action has a much better feeling in terms of touch and control.