If the toilet flush handle sticks, replace or adjust it.
If you think your toilet flapper is leaking, add a few drops of food colouring to the toilet tank (but don’t flush). If the colour appears in the toilet bowl, you have a flapper leak that needs repair.
Install a showerhead that allows you to stop all but a trickle of water while you lather up or shampoo. A showerhead with a "trickle" button allows you to resume the same flow rate and temperature.
Don’t flush paper waste down the toilet if it can go in recycling, compost or garbage.
Turn off the tap while brushing your teeth, shaving or washing your face.