How to switch between windows

In "System Settings.." --> "Keyboard" go to 'Shortcuts' tab. At the left choose "Navigation". Scroll down to "Switch windows of an app directly", and assign the keyboard shortcut you'd like (I'm using Alt+'). Hope that works for you.

At least in 13.04, you should be able to do this with alt+§ (the key above tab, at least on Swiss keyboards).

I discovered two ways of doing so.

1. Use alt+tab until the desired app gets marked. Then wait a little while until the seperate windows of the application show up.
2. When you have one window of the application active, click on the applications icon on the quick launch bar. You should now see all of the applications windows.
3. To switch to the previously selected application hold alt und press shift+tab

Another suggestion is switching between workspaces.
Just put a window of your application on several workspaces. You can switch between these workspaces really fast using alt+ctrl+arrow-key(up, down, left, right).