preferably an olympic bar with weights each side, I would say use a 20kg plate each side as the first plate on then you get a nice lifting base, but any would do I guess, although it might look funny doing it with 5kg plates...
I agree that you need to get your technique right but I find that with an empty bar my technique is thrown off and I get a better feel when there is a bit of weight on (not too much though)...