Ranieri was appointed by Watford after Xisco Munoz was sacked seven games in the new Premier League season.
His departure made the Spaniard the 13th coach to leave Watford since the Pozzo family bought the club in 2012.
Ranieri is the latest manager to head to Vicarage Road and he has set himself the goal of keeping the club in the top flight.
“I feel good, luckily I feel good. When I think of football, I feel good every time. Football is my life and I am very happy, ”said Ranieri.
“I am very happy to come back to the Premier League, one of the best championships in the world. I’m an ambitious man and I hope to get Watford to be safe at the end of the season – and also to improve and increase for next season.
“We have to be safe and then slowly, slowly, go up. The program is very good, very ambitious.
“He [the owner] is ambitious, I am more ambitious. Hope our bond is fantastic for Watford, for our fans.
“I am now thinking of 40 points. I don’t know who I can hit those 40 points against. There are 33 points to reach now because we have seven points. We need to reach 33 points, I don’t know against whom. I want to fight.
Speaking of Watford’s reputation for shaking up managers, Ranieri added: “In Italy it’s okay to change managers. There are three or four teams that change managers.
“We have to do our best, I can’t think of the old manager. Xisco was my player in Valencia, I hope he can find a new solution very soon. Now I have to do my best for Watford.