One thing that I have picked up on, is always put the song that you think is the best as your first song on the CD. Generally if somebody receieves lots of Cd's and they don't have a lot of time, the tendency is to listen to the first song on the CD. If the person listening enjoys that, then you stand a better chance of it getting on the radio.
Its IMHO the same as sending a CV. If you haven't caught the eye of the reader instantly, you stand a good chance of it getting binned immediately.
Finding out about the person who will play your song and their tastes, helps you to direct their attention to a song on the Cd that you think would suit their taste.

I'll get me coat