Help my toilet doesn't Flush completely the first time or second time
educate kids/occupants not to put anything into the toilet bowl other than


normal bodily excreta.
minimal amounts of toilet paper. (n.b. wet-wipes etc can cause partial blockages)

check the fill level in the cistern/tank, adjust as needed.
replace the flush valves in the cistern/tank.
clean out the inlet holes around the rim.
use a limescale remover in the bowl and in the tank.
snake the sewer pipe.
replace the whole thing.