How to improve gas mileage on my Audi A4?

I notice that my Audi A4 doesn't get the best gas mileage. Are there any tips or tricks to improve it?

Regularly check and replace your air filter. A dirty air filter can decrease your gas mileage by up to 20%.

Make sure your tires are properly inflated. Under-inflated tires can decrease gas mileage by 0.2% for every 1 PSI drop in pressure.

Avoid unnecessary idling. If you're going to be sitting for more than 10 seconds, turn off your engine to save gas.