These techniques will do the trick:
• Break up larger lumps by whisking the gravy vigorously in a figure-eight motion.
• Pour the gravy through a mesh strainer. Avoid pressing flour lumps through the mesh.
• For small, stubborn lumps, puree the gravy in a blender or food processor.
Starting with sure-to-be-perfect gravy techniques is a good plan, too. Check out our step-by-step gravy-making instructions.