A few suggestions, some of them airport specific:
(a) In Canberra, signage (so that one can find where the different things in the airport area), and in the boarding area, signage that is readable about what flights are departing from where. It really is about the worst airport that I have ever been to
(b) Showers - a facility that one pays for would be fine, and with good quality facilities - in arrivals: there seems to me little worse than a long economy flight (especially overnight), without one being able to freshen up on arrival
(c) Good quality, uncrowded food courts: Singapore's basement food court in Terminal 3 is a really good model for this
(d) To get rid of all the duty free shops which clutter up ones passage to the planes. Sydney is terrible on this score - one has to go through a huge shopping area before one can get to actual departures. I'd be happy to see the end of duty free completely: given that space in aircraft is at a premium, why encourage people to take on board all kinds of expensive rubbish. (I'd also be delighted to get rid of it on planes, and have the cabin crew spend their time providing actual services to the passengers, instead.) It would be fine - as in Sydney and a few other places - to have duty free in arrivals, provided that it was not obtrusive. This is not a proposal to remove shops from departures; just to have shops that sell things that people would actually wish to consume before or during a journey.