Forestieri joined Watford on loan from Udinese in the summer and helped the home side move up to 15th on the back of their third home win of the season.
Zola said: "He is a young player who has got a lot of potential but he needs to learn to use this potential.
"Sometimes he doesn't but we are here to help him and I am sure he will become better and better. I feel there is a lot more to come from him.
"It was very good to win against a really strong side who are one of the best teams we have played against.
"They made it very difficult for us but there were times in the game where we played very well.
"It was a good performance and I was really pleased with it."