When you do a media interview, it is important to know why you are doing it and what it is you want to say.
But in preparing your ‘key messages’ it is important to remember that you must not just learn them, you must think about how you deliver them.
Just parrot your message
Just ignore the question
Forget that listeners and viewers nowadays are sophisticated and will recognise attempts to railroad the interviewer
Use bridging phrases to turn your answers into opportunities to deliver your messages
Vary your phraseology
For a good example of how not to do it, watch this interview with Ed Miliband concerning public sector strikes: