As a general rule in Italy, if the view is spectacular the food and service will probably be mediocre. That doesn't mean that sometimes it's not worth the risk and extra euros and that sometimes you will be surprised.
If it's morning or early afternoon have coffee or hot chocolate at the shabby chic Caffe Florian. If is five o'cock somewhere, head straight to Cafe Quaddri for an extravagant cocktail.
The menu is the size of a fall fashion magazine, the drinks are flashy and expensive(though the snacks are a little weak) and they serve the best dirty martini I have ever had.
Add great company, a summer Venetian sunset and the orchestra in the background and you have perfection.
Piazza San Marco, Venice
+39 041 5222105