Australia has topped the medal table in 12 of the 19 Commonwealth Games since the inaugural Empire Games in 1930.
But Coffa, who was played a key role in bringing the 2018 Commonwealth Games to the Gold Coast, told the Forum that past performance is no guarantee of future success.
"The trend we are seeing is more Commonwealth nations winning medals of all colours as the overall standard of competition gets tougher," the ACGA President told the Forum.
"Even in sports where Australia has traditionally produced significant numbers of medallists, that dominance is being slowly chipped away.
"We saw that at the recent Olympics and the Commonwealth Games will be no different.
"It is important that Australia does well at a home Games but to achieve that we will need to work harder and smarter to stay on top.
"Preparations for 2018 need to start now."
Athletes such as swimming superstar Ian Thorpe have helped Australia become one of the dominant forces at the Olympics and Commonwealth Games over the past decade but the country's stock has fallen in recent years, particular when they finished tenth on the medal table at the London 2012 Olympics with just seven golds.
But as well as targeting medal success at Gold Coast 2018, ACGA chief executive Perry Crosswhite said the success of the next Commonwealth Games in Australia will be judged on several factors.
"For the ACGA, the definition of what makes a successful home Games is about more than just medals," he said.
"It is also about the lasting legacy it creates for Australian sport.
"Sporting infrastructure and giving our young athletes a taste of major competition are the most obvious examples.
"But we are also saying to sports that we should be emerging from Gold Coast 2018 with more trained and experienced coaches, administrators and technical officials.
"That will ensure that the investment made in these Games - and in the Australian team - generates the maximum benefit for the longer term development of sport in Australia."
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