What are the likely culprits for low fuel economy in my used SUV?

[Chloe5]

I recently bought a used compact SUV for commuting and light family trips, but I'm consistently getting significantly lower fuel economy than the EPA estimates and what the previous owner claimed, even with conservative driving. I've checked the tire pressure and changed the air filter, but the mileage hasn't improved. For others who have tackled this issue, what are the next most likely culprits to investigate, such as oxygen sensors, fuel injectors, or alignment, and is there a reliable way to diagnose the problem without just throwing parts at it?