South Africa rose to number one in the world after the 2-0 series win against England and Smith has said that they need to improve to stay there.
"We will face different challenges but we have a formidable squad that performed outstandingly well here," The Telegraph quotes Smith as saying.
"We need to grow that. We are a humble team. We are not flashy and it will be about hard work."
South Africa also top the Twenty20 world rankings, just one point ahead of England.