The first rule is they should be cooked as briefly as possible. Cook them with such things as eggs, chicken, fillet of beef, pasta, rice or potatoes, to provide a rather gentle background for their perfume, rather than with ingredients with strong flavours, which will smother them.
Leaving whatever ingredient you are going to use in your truffle recipe inside an airtight box with the truffle allows the aromas to start working their magic. This works extremely well with eggs (particularly if you wash the shells first to make them more porous) and with rice, but you can also, for example, put slices of the washed truffle inside or under the skin of an uncooked chicken for a few hours or overnight in the refrigerator.