How can I switch between windows of the same application?

This is old question, but I had the same problem and found Alt + ` switches the windows of the same application. Thus, sharing the same for reference.

If you install the CompizConfig Settings Manager then you can access and change the Compiz settings that can do this. Once installed launch it via System->Preferences.

If you normally use Alt+Tab then go the "Static Application Switcher". (This plugin shows quite small previews.)

If you normally use Windows/Super+Tab then go to "Shift Switcher Plugin". (This plugin shows quite large previews.)

In the settings for either of the plugins you can set the keyboard (or mouse) shortcut for Next Window (Group) and/or Previous Window (Group).

(Note: as well as the Static Application Switcher and Shift Switcher you may wish to experiment with the Application Switcher and Ring Switcher)