If u have more than one printer, can select which will be the default one
Click Session menu of the top panel & click System Settings.
Now click printing under Hardware category and right click desired default printer from the list of available printers, and click Set as Default. When u print the default printer is automatically used.

U can also use command line tool, lpoptions: http://manpages.ubuntu.com/manpages/natty/man1/lpoptions.1.html