What should I check first if my pool pump is sucking air?

Check the pump lid O-ring first — it’s the most common cause of an air leak on the suction side. Turn off the pump, clean the O-ring groove, and inspect for cracks or flat spots; replace if worn. Apply a thin coat of pool-specific silicone lubricant, and ensure the lid is hand-tight. Also verify the pool water level isn’t below the skimmer and that baskets are clear.