Sarkozy, 60, faces an uphill struggle as he tries to see off more popular members of his party, The Republicans, in order to make a new bid for the presidency in May 2017.
His new book, "France for Life", blames his defeat at the hands of Francois Hollande in 2012 on his failure to get tough on France's famously generous benefits and heavy taxes.
"Today, I regret delaying some reforms that should have been made in the first days of my presidency," writes Sarkozy, who ran the country from 2007 to 2012.
Actor Gerard Depardieu and rock star Johnny Hallyday are among those who have left France in recent years to escape its hungry taxmen.
Also Read
Sarkozy also acknowledges his reputation for being short-tempered, regretting that he "gave into anger" on occasion, such as the time he was caught on camera mumbling "Get lost, you stupid bastard" at a man who insulted him during an agricultural show.
He now says he was trying to save his marriage, which soon ended in divorce and led to his much-publicised relationship with singer-model Carla Bruni, now his wife.
"I should have anticipated better, and been more cautious, and put my new status as president before everything," he writes.
Sarkozy makes no secret of his ambitions to return to the Elysee Palace.
"With this book, Nicolas Sarkozy is not offering his memoirs, he is giving us a self-examination designed for an eventual return to power," the daily Le Figaro wrote on Friday.
It took only two years for him to change his mind, returning to lead the UMP party -- which he renamed The Republicans -- and lining himself up for another possible run at the presidency in May 2017.