One of the best ways to see the wonderful palazzi along the grand canal is to take a vaporetto ride. Grab a seat with a view near the end of the line and enjoy a ride up or down the length of the canal. The ticket will cost you 6.50 Euro, if you don't have a pass, and is a great way to relax and see the sites.
Give yourself a second treat and take the same ride at dusk or after dark for another perspective of the palazzi when they're lit up. Best to get aboard near the ends of the line for the full effect.
Piazzale Roma and the Accademia stops are good spots.