What to do with one full day in Las Vegas?

Depends on what you like to do, I love spending the day playing poker in a casino but I know that isn't for everyone.  Walking the strip like has been mentioned is good, If you want to go off strip and see some incredible scenery I'd recommend checking out Red Rock Canyon National Conservation Area.  Seeing the city from high above the city at either Stratosphere Casino, Hotel & Tower or High Roller is a great way to see a lot in a short period of time.  

Like Rocio mentioned, I'd start at one end of the Strip and just make your way up/down it. Walk into some of the hotels, check out the fountains at the Bellagio Hotel, the Siegfried & Roy's Secret Garden & Dolphin Habitat at the The Mirage, go for a ride on the world's tallest wheel at the High Roller, have lunch at one of the most popular restaurants, Giada, crash a pool party, such as Mandalay Bay Convention Center, and do a show, such as Absinthe or Cirque du Soleil, which has shows at several of the different hotels. There are also a couple different kiosks that do half-priced shows on the day of the shows. Then I'd do a nice dinner and drinks, perhaps at ARIA Resort & Casino and The Cosmopolitan of Las Vegas at The Chandelier.

Hello Pippo. Easy! Walk Las Vegas Strip and take a look at every hotel resort and casino along its route. The architecture represented on every hotel is exquisite plus the entertainment you find inside their walls is amazing. The indoor and outdoor gondola rides at The Venetian, the Bellagio Hotel fountains or shopping at the unique Forum Shops at Caesars plus many other attractions will make you enjoy the day. If you want to do something different, you can take a 1 day tour (which I did) to the Grand Canyon Tour Company. It is a bit tired but it is worth it.

Hope this helps!!

I would get a spa service at MGM Grand Las Vegas put my things in a locker, put my suit on and go hang out at the pool. I can spend all day chillin at their pool and dining.

the best bang for the buck, is get a day pass and take the bus from MGM Grand Las Vegas to Downtown. Then walk a half mile to the outlet mall and go shopping. Walk back to the bus and take it back down the strip to the Bellagio Hotel. Cross the street to the Paris Las Vegas, after you view the fountains.  

Eat in front of Bellagio Fountains at the Paris Hotel.  

You can walk through the Paris Hotel and go up The Eiffel Tower. There is a photo op on the way. Then walk to the back, through the malls into St. Mark's Square at The Venetian. Look for the Gondola ride. It is approx $20, well worth it. Sign up for the rewards card at the Paris, and the Total Rewards Credit Card there.  

Walk down to the MGM. Sign up for the rewards card and apply for the MGM credit card then. 

Take the Bridge across to New York New York Hotel & Casino. Take pictures from there.  

Walk through and go left to the bridge to Excalibur. From there, you can find the trams to Luxor Hotel and Casino and Mandalay Bay Resort and Casino. Or you can choose to walk to the Tropicana Las Vegas - a DoubleTree by Hilton Hotel. Go to any valet and take a cab or shuttle back to the airport.