Why is my Vauxhall Grandland's fuel efficiency decreasing?

I've noticed that my Vauxhall Grandland's fuel efficiency has been decreasing over the past few weeks. What could be causing this and how can I improve it?

One reason for your fuel efficiency decreasing could be due to poor tire pressure. Make sure to regularly check and maintain the correct tire pressure.

Another possible reason could be a clogged air filter. Check and replace the air filter if necessary to improve fuel efficiency.

It could also be due to excessive idling. Make sure to turn off your engine when parked and avoid prolonged idling.