Hi Yunita - I'm going to Italy in May but I've been there twice before. You might want to expand your comment to include where in Italy you are going and what kinds of things you want to do.
As far as sightseeing, my general tips would be:
- book tickets and tours in advance. Otherwise you'll stand in line waiting for hours to enter popular destinations.
- Learn as much as you can about the places you will see. My (then) wife and I walked into a small church in Rome and my wife just kinda glanced around. I pointed to a sculpture and said, "Did you realize that was created by Michelangelo?" Totally surprised her. She didn't expect to see original art by Michelangelo in a little church. There is SO MUCH art and history in Italy, it really helps and provides perspective if you have a little info at least about where you're visiting.
- Plan your sightseeing geographically. Target a few destinations that are close to each other each day. You spend less time bouncing around the city and more time seeing destinations. I broke Rome up into quadrants on one trip and we targeted a quadrant each day. We saw a LOT of sights that way.
- Did I mention scheduling and buying tickets in advance? For popular destinations like Coliseum or Accademia in Florence (to see Michelangelo's David), you want to buy tickets WELL in advance. You could be buying them right now for your trip this summer.
- Learn some common phrases in Italian. Also watch Youtube videos on things NOT to do or wear in Italy. Like, don't enter a church with bare shoulders or shorts. They are likely to turn you away.
So - where are you going, how long will you be there and what do you want to do there?