Nice is a big city, it would be hard to explore it all on foot in one day! Renting an electric scooter will give you more time to explore the different spots of the city in all convenience.
Avoid traffic jams and start by riding along the sea on the Promenade des Anglais. Then go explore old Nice and its picturesque Cours Saleya market, restaurants and colorful little streets. All about the views? Ride all the way up to the Castle hill and admire the magnificent panorama.