The Serbian star enjoyed a spectacular 2011 campaign, winning three Grand Slam titles and finishing the year with a 70-6 win-loss record.
Speaking in Abu Dhabi, where he due to open his new season in the Mubadala World Tennis Championship exhibition event, Djokovic said: "There's still room for improvement.
"That's something that I am aiming for. The game that I have is good enough to be one of the best on all surfaces so I just need to maintain that level and always improve certain strokes in my game by certain percentage."
Asked whether it would be possible to repeat his achievements of 2011, he added: "Why not? I think it does not make sense to be anything else than optimistic.
"I need to believe in my qualities, in my abilities. I need to believe I can repeat this year again. Of course, it's going to be an incredible and a difficult task to achieve, but you never know. Nothing is really impossible."
Djokovic will play Gael Monfils in his opening match of the season on December 29.
Rafael Nadal and Roger Federer are also in the six-man Abu Dhabi field.