The France striker endured an injury-plagued first year in England after suffering a knee injury in preseason.
"I am feeling better after the difficult season last year. I am feeling better," Nkunku told chelseafc.com.
"I had a nice break during the summer. I needed it. I worked a little bit before coming here, but it was important for me to break after this year, for my head also. It was good.
"Now I am working in every training session to stay fit and to go forward in a good way. Pre-season is very good and the team is good. We are practicing the hard work to be fresh and ready to play some friendly games."
On new manager Enzo Maresca, Nkunku continued: "The new head coach brings very good ideas to play,’ says the 26-year-old. ‘We are all happy to practice every training with him. Now it is just the beginning. We need to learn and to fix in every training the way he wants us to play.
"We are on this way to learn. If everybody has the idea of the coach to play, we will produce good football this year.
"We are playing with the ball already a lot. As he told us the first day, he wants us to be on the pitch to practice football training directly. His idea is to keep the ball, so we are practicing that now."