i started on day 1 by leaving my dog in a separate room (with use of childgate so she could still see and so wasn't distressed) for a few seconds and then minutes, also the next few days went into the garden for a few seconds then came back in. Ignored any howling but returned when she was quiet with lots of praise.
Then graduated to popping to the corner shop, adding on 5 minutes here and there - but NOT always longer, sometimes i still popped out for just a very short time, otherwise all you are teaching is that you will be away for longer and longer

In spite of being a breed that wants to be with you, she has enough independence and confidence to be able to deal happily with any disappearances from me.
I also stuffed lots and lots of Kongs and Funballs (with mini markies) to keep her occupied.
Lindsay