Are you using the correct cycle selection for fabric type?
Use a higher soil level cycle option and warmer wash temperature to improve cleaning.
If using Quick Wash cycle, wash only a few items.
Use Whitest Whites or Heavy Duty cycle for tough cleaning.
Add an extra rinse for heavily soiled loads.
Is the wash water temperature too low?
Use hot or warm washes, if the warmer temperatures are safe for the fabrics. Check the fabric care labels for temperature recommendations.
Check that the hot water fill hose is connected to the hot faucet and that the cold water fill hose is connected to the cold faucet. Both faucets must be open all the way (turned on) for the washer to operate properly.