Renault Kangoo Van - 2001 X - Fuel Economy?

I have just purchased a 2001 Kangoo 665 Van, however I dont think im getting any where near the correct economy out of a tank of Diesel.

Currently getting about 350miles/Tank

Can anyone advise :

a) The correct MPG figure for the van as at build, (Yes I expect some MPG loss but I would expect to be getting 500 + Miles / Tank)

b) What I can do to rectify this. (I know driving style has a lot to do with economy, but I'm not a "heavy Right Foot" driver.)

All Help Very Much Appreciated