The 25-year-old, who moved to the Stadium of Light from Wolverhampton Wanderers in the summer, has netted five goals in four appearances for the Black Cats so far.
"I kind of keep it to myself," the Shields Gazette quotes Fletcher as saying. "The first thing is to do better than last year, and if I can keep improving that will keep me happy.
"I just go out and play the game the best way I can, and I do not like putting that kind of pressure on myself."
Fletcher found the net 12 times for Wolves last season.