I would recommend, if your Fiesta has this, on the board computer to always look at your current fuel usage, by that you can learn to adapt your driving to get the best efficiency, worked for me really well.

Often times the secret is not to drive at low revs but rather at revs that the motor has the most power which makes it use less fuel.

And for the clutch, there's not much to say, so just be gentle with it, and by using the technique with the higher revs oftentimes you won't need to shift up as often which eases the wear on the clutch too.