Have your holding tank cleaned every 6 to 12 months.
Install a low-flow shower head in your shower/bath to save water.
Repair leaking taps.
Spread your washing out over a few days to reduce the load on the greywater sullage absorption / transpiration / aspiration area.
Extend the life of your trench and avoid blockages by using lint filters in the laundry - a stocking over the outlet hose will do.
Use hot water in the laundry to give a more efficient wash
Don’t leave taps running unnecessarily, for instance when cleaning teeth.