Soil level (Heavy, Normal, Light): Separate clothes according to soil level. If possible, do not wash heavily soiled items with lightly soiled ones.
Colour (White, Lights, Darks): Wash dark or dyed clothes separately from whites or light colours. Mixing dyed clothes with light clothes can result in dye transfer or discolouration of lighter clothes.
Lint (Lint producers, Collectors): Wash separately lint producing fabrics from lint collecting fabrics. Lint producers can result in pilling and linting on the lint collectors.