Thaksin, whose return home last week was made possible with the election of a new government, told the Financial Times the coup 17 months ago and the political uncertainty that followed have seriously damaged the country's image.
He said the new government, which took power after a smooth transition from the military rule, would face a tough time in re-establishing investor confidence.
"Confidence is very expensive economically," Thaksin told the newspaper. "When it's gone, it will cost a lot of money to bring it back -- and time, not just money."
Thaksin, who has promised to stay out of politics, said, "If I were to help the government, I would probably create more problems than (I would) solve."
He said Thailand should take advantage of the rising value of the baht to buy capital goods from abroad rather than worry about its impact on Thai exports.
Thaksin had been charged with abuse of power when he held office but he denies any wrongdoing.