Ninety minutes is a very long time in televised political debate and slip-ups can happen. Gone is the cosy one-to-one interview in which key messages are carefully delivered and deftly fitted into the allotted on-air time. In its place is a gladiatorial arena with a live audience, blindingly bright studio lights, and numerous microphones and camera angles that pick up every verbal nuance and non-verbal tic. Admittedly, Messrs Brown, Cameron and Clegg are no strangers to head-to-head sparring. They face each other at Prime Minister's Questions every Wednesday. But the messages they want to send out to the public at large will be affirmed, or undermined, by what they don't say – just as much as the policies they promise to deliver.
Before each political leader steps up to his studio podium, he will have spent hours behind the scenes going through "simulated combat". But the more you prepare, the more likely it is that you will appear wooden and scripted. According to Michael Sheehan who, since 1988, has been called upon to coach every presidential and vice-presidential debate in America, success can lay in the difference between performing and acting. Performing involves delivering messages effectively to millions of people, but acting can have the ring of insincerity about it, and the voter wants a sincere leader.
The likeability factor is key to any debate, and whether or not the camera likes you will play an important role in winning people over. Picking your nails, wiping your hands through your hair, or darting your eyes from side to side are all distracting and displeasing for the audience. So is the temptation to avoid answering a question by replying with a patronising: "The question you should be asking is..." which merely illustrates that you're opting out. Voters want smart, not smug, answers. So a statesmanlike performance in which the participants avoid cheap attacks on their opponents, are prepared for the inevitable questions about their mistakes, and appear in command of Britain's future will all gain credit with the viewer.
* Watch your facial expressions. The "chin drop" makes you look nervous
* Inject personality into the debate to win over the audience
* Be ready to admit a mistake
* Look interested in the views of your opponents
* Keep within time limits. Running over time limits is resented by viewers
* Avoid cheap attacks on your opponents
* Pay tribute to opponents' successes. It shows you are statesmanlike
* Avoid sticking your tongue out, known as "lizard tongue". It suggests nerves
* You have a good smile but a weak laugh. Use the smile
* Use stories instead of statistics. Voters remember stories not numbers
* Look statesmanlike. You lack experience and must work hard to win the trust of your audience
* Communicate congruently. Your gestures can undermine your intended messages
* Look at your opponents when they are speaking. Voters want to see that you are fully engaged with the debate
* Breathe deeply, shoulders back, back straight. Don't be outshone by your more aggressive political rivals
* Joke at your own expense. People like those who are confident enough to do so
The writer is a former BBC news anchor and media trainer