Fuel consumption

[Hmc1]

Hi all!, so 2011 diesel . I think it uses far too much fuel , more than my Kia 2l , I’m trying not to drive it like the Kia ie thrashing it to go as quick . I’m keeping an eye on the gear change arrow thing too 

I’ve checked fuel receipts and also going on the guage  it’s saying ave of 39-40 mpg 

that seems terrible , I’m not sure I can keep it being a self employed cleaner driving all over . I do do a mix of longer and short journeys with a motorway trip now and then . I ignore the thing that’s telling me how many mpg at that moment as it makes no sense, ie shouldn’t motorway be better to gallon ? It dosnt show that it’s very random from 20 - 40 

thanks so much as always from a clueless driver ! X