The Prime Minister also admitted he could present the Government's message "a lot better", adding: "I'm actually shy by nature rather than extrovert."
During an interview with Piers Morgan for the latest edition of GQ magazine, Mr Brown defended his record in Afghanistan, insisting "I am a friend of the military".
Despite saying Simon Cowell deserved the tens of millions he earned, he said there was a feeling of "unfairness" over the sums of money being paid to TV stars.
When asked "is it right that someone like Jonathan Ross gets £18m from the BBC?", Mr Brown replied: "The BBC has got to seriously consider its salary structure."
Mr Brown said he wanted to be involved in charitable work when he leaves office but refused to condemn former prime ministers for doing speaking tours.
He said the upcoming election was the first "big-choice election" of the global age.
After Morgan claimed the public perceived him as miserable and dour, Mr Brown said: "I accept I have to do better in the presentation area. I've got my strengths and I've got my weaknesses."
Brown said his strengths were "that I make big decisions and I'm not afraid of breaking new ground" but admitted: "Well, I could present our message a lot better, I'm actually shy by nature rather than extrovert, someone who feels that your actions should speak for themselves, but that's not the way politics works these days."
The PM said he was not bothered about recent controversy over Andrew Marr asking him if he was taking medication.