The Blues gave their title hopes a boost at the start of the week by becoming the first team to win at the Etihad Stadium in the league this season.
However, Luiz believes that the side still needs to improve if they want to be serious challengers come the end of the season.
"We need to keep working hard and keep our feet on the floor," the Brazilian told the club's official website. "It was just one more game and three points. You have to improve every day if you want to win the title.
"When you play against a strong team like Man City you can feel the importance, but in terms of the table it's just another three points, that's the truth."
Chelsea return to Premier League action on Saturday when they welcome Newcastle United to Stamford Bridge.