Just put some pictures up and a nice coat rack.

Paint the walls or the door, create some contrast. A large floor mat with some of the chosen colour in it will help or if it's in your budget, I'd think about putting in a new floor. The one that's there is very sterile , does nothing for your foyer.

How about a large plant to the left if the door and I agree with the other comments about a rug and contrast paint. Photos with different interesting frames up the stairs will add interest

To what extent - low budget and work with what you have with the fixed elements?

Agree with oneofeleven paint the door and the window frame above it.... Possibly black! Then add artwork with black frames .

A rug would be nice for guests coming in so that they can wipe their feet and not feel as if they are tracking in debris or rain. Perhaps a round one...

Add some family pictures going up the walk or and city out some cut out some niche spots