Jessica told CBBC Newsround Online: "There was no doubt in my mind that I wanted to be a part of this campaign.
"It's very important to target youngsters. Once you start it's really difficult to stop."
"By showing that I'm supporting this hopefully young people will see that it's not a good thing to be doing."
The lessons on how to help your mates will be taught to secondary school kids as part of PHSE or Science class.
Research shows that 10% of kids aged between 11 and 15 smoke regularly.
Jess also had time to tell us all about her musical plans for the future.