Remember, loose parts absorb the sound. Eliminate loose parts whenever possible. Finally, the tone ring should fit so that if you have the tone ring on the rim, and you turn this upside down on a table, that you can lift the rim out of the tone ring. Otherwise, the rim will not lift out of the tone ring under any circumstances. This should also be done on a humid day.
Humidity affects the fit.
The fit should be a slip fit, but not a wobbly, loose fit. Also, make sure the neck does not contact the tone ring at the heelpiece, if possible. The reason for this is to allow the skirt of the tone ring as much vibrational freedom as possible. When I first posted this information, several people asked about it, mentioning that the cut of the heelpiece was such that contact was unavoidable. If this is the case, don't worry about it.