Hello fellow auto owner. Also to bare in mind is pre 2012/3 fiestas have an old school 4 speed automatic which isn't know for good fuel economy.
My mpgs fall through the floor during these winter months when doing short city stop & go commutes from a cold start. As James has said it should improve over time, and as daft as it sounds my mpg is much better in the summer months.
To be honest though if you're looking for good fuel economy from the 1.4 petrol 4-speed fiesta, you're going to need a steep decline, and a strong tail wind lol.
Having said that I think my best ever reading was something like 48mpg - but that was on a single journey, rather than an average over a whole tank of fuel.
Post facelift (auto) fiestas now come with Ford's Powershift, a 6 speed twin clutch automated manual gearbox which gives much better mpgs than it's predessor.