Be sure about that the packaging is strong enough, so it can protect the cd or dvd. Unfortunately it is not rare that we receive badly packaged mails, where even the data medium is damaged, when of course it’s unusable.
Label everything precisely. Be sure that there is information about the band name, songs, etc. Probably the best, when you enclose a letter, which shall contain the name of band, the name and order of the songs, and any comment that you feel can be important to know.
When writing the media, please pay attention to that the disc should be closed (no multisession, so no further writing is possible), or else different problems may occur at our side. The easiest way to be sure everything is fine is to load back the media to the computer, and check with a filebrowser if it can read well. Never stick anything onto the surface of the disc. It might look impressive, but it can easily damage the media. Don’t write audio cd, it’s not suitable for mastering. Always write in disc-at-once mode and whether burn a data dvd, or data cd (data cd or mac/pc hybrid). If possible, the maximum writing speed should not be more than 16x, this way you can have a troublefree written media.