Highest impact first
- Seal duct leaks, especially return leaks pulling hot attic or crawl space air into the system
- Clean the outdoor coil so the system can reject heat on hot afternoons
- Restore airflow with a properly sized filter and a clean blower and evaporator coil
- Verify refrigerant charge, since both undercharge and overcharge waste energy
- Add attic insulation where it is thin, which reduces the load the system has to meet