Cube the bread the day before or the morning of the meal and leave it out to dry slightly; this helps it hold up better in the hot cheese.
If you cannot find Tomme cheese, substitute with more Beaufort or Gruyère.
Use a wooden spoon for stirring to prevent scratching the pot and to help emulsify the cheese.
If the cheese bubbles rapidly, lower the heat of the burner to prevent separation.
Traditional fun: Establish penalties (such as buying the next bottle of wine) for anyone who drops their bread into the pot.