What the leaders learned from Monday night's debate

1. It pays to be polite, and dull

The debate between the three would-be chancellors was pretty boring, especially for those viewers who dutifully sat through the whole hour. Prime Minister's Questions in the Commons is livelier, because there the party leaders go for the jugular and whip up their supporters into a frenzy of excitement. That sort of behaviour works in the hothouse of the Commons, but the public does not like it. They want politicians to be polite. Politeness makes dull television, but politicians need not worry about that.

2. They must never get angry

Part of the ordeal for the politicians is that the cameras are trained on them for the whole hour, whether they are speaking or not, so if they show a flash of anger at something an opponent says, everyone will see. The skill is to treat the whole discussion as a quiet disagreement between friends.

3. Or be patronising

George Osborne tried to squash Vince Cable at one point by reminding that, whatever else happened at the election, it was not going to result in a Liberal Democrat government. True enough, but it was not well-judged of Osborne to say so.

4. Humour works

Alistair Darling should have had an awkward moment when Osborne accused him of plagiarising a Tory policy. He said: "In your Budget last week you introduced one tax cut, which was taking first-time-buyers out of stamp duty, which I proposed a couple of years earlier. Do you acknowledge that?" It was true, but the public does not really care who thought of it first, if it is the right thing to do. Darling swatted the question away by saying: "Nothing like cross-party agreement, George – we're all in favour of that," which earned Darling his one and only spontaneous round of applause of the evening.

5. So have a good one-liner at the ready

Neither Gordon Brown nor David Cameron would make the mistake of going into Prime Minister's Questions without having a scripted joke which can be pulled out at the right moment. But it had not occurred to Darling or Osborne to come prepared in that way and therefore it was left to Vince Cable to deliver the evening's only memorable one-liner, on bankers who threaten to emigrate rather than pay higher taxes: "This country was held to ransom in the 1980s by [the miners' leader Arthur] Scargill and people like that and now we have got these pin-striped Scargills threatening to blackmail the country." Not a very good joke, but at least it stuck in the mind.

6. Twosies beats onesies, but nothing beats threes

Having three participants – rather than two, as in US presidential contests – changes the dynamic. It worked to Vince Cable's advantage. Since there was very little risk that the other two would ever gang up on him, he could choose when to side with Alistair Darling, or George Osborne, or neither. This is not always a good position to be in, because you can be made to look like an irrelevance if your opponents just argue with each other and ignore you, but Cable is too experienced an operator to fall into that trap. Nick Clegg may find it harder to stay afloat.

7. David Cameron may look lonely

It was noticeable how Vince Cable ganged up with Darling against Osborne much more frequently than with Osborne against Darling. The best outcome for the Liberal Democrats in this election is a hung parliament, so it makes sense for them to concentrate on discrediting the Conservatives. If Nick Clegg follows the same tactic, it could make Cameron look isolated. But if he is astute, he will turn it to his advantage by making himself look like the man they are both trying to stop because he is making the running.

8. It helps to be the underdog

If anyone was going to make a pig's ear of that first debate, it was assumed that it would be George Osborne, the least sure of the three performers. The fact that he held his own meant that the verdict on his performance was more generous than it would have been if expectations had been higher. David Cameron will not have that advantage. People expect him to outshine Brown and Clegg, so he may have more to lose.

9. The best questions are the ones they do not expect

After a consultant in the audience had asked about the future of his A&E ward as public spending cuts begin to bite, both Darling and Osborne repeated the promise made by their leaders that the NHS budget will have special protection. Cable, by contrast, said that it would be wrong to promise that any government department will be exempt. At this point the Channel 4 presenter Krishnan Guru-Murthy bowled a googly by inviting Osborne to explain to Cable why NHS funding needed to be ringfenced. It is not a question he ever expected to be asked, because politicians naturally assume that no one is in favour of cutting the NHS, and could only answer that Cable could "speak for himself".

10. That's why the leaders' debates will be even duller than the chancellors'

In the party leaders' debates, the presenters will not be allowed to put any questions of their own. Questions will come solely from the audience, with the presenters acting as moderators only. This will protect the leaders from the sort of sharp questions put by Krishnan Guru-Murthy, which helped prevent the meeting of the would-be chancellors from descending into total tedium. That makes it all the more likely that the leaders' debates are going to be very dull affairs – unless, of course, someone either has a flash of brilliance, or bombs so badly that it creates a memorable television moment. Whether such memorable moments are good for democracy is another matter.