How to maintain the fuel efficiency of a Ford Fiesta?

I've noticed that my Ford Fiesta's fuel efficiency has been decreasing lately. What are some tips and tricks to help maintain its fuel efficiency?

Regularly check and replace your air filter. A clogged air filter can decrease fuel efficiency.

Make sure your tires are properly inflated. Under-inflated tires can decrease fuel efficiency.

Avoid idling for too long. Turn off your engine if you're going to be parked for more than 30 seconds.