The 26-man team is training at its base in Arnhem to polish up ahead of the friendly match against Holland in Rotterdam, May 31, reports Xinhua.
"There is this kind of competition... no one is sure of himself at the moment. Everybody is attentive to whatever is taught in training. Everyone tries to do whatever he can and, for me, it's good for the team and I am really impressed," Appiah said in an audio message here Wednesday.
Appiah believes the team's pre-World Cup preparations have been good so far, saying the players have shown exemplary discipline in their quest for success at this year's most-watched global sporting event.
"The key to success is discipline. Discipline plays a big role; if you want to be successful, hundred percent lies with the players' behaviour and so far it has been good," he said.
Appiah will name his final 23-man squad after the friendly game against the Netherlands before Ghana continue their journey to Miami via Washington DC, June 1.
Ghana has been drawn in Group G of the FIFA World Cup alongside the United States, Germany and Portugal, and will play its opening Group game at the Arena das Dunas in Natal against the US, June 16.