Use a Back Pressure Valve to apply consistent pressure on the check valve balls so they close promptly and firmly.
Ensure there are no air bubbles trapped inside the pump chamber or anywhere else in the discharge line. The air bubble will compress and expand without pushing the liquid through. Remember gas / air is compressible while liquids are not compressible.
Use a degassing valve installed on the pump head when pumping a chemical such as sodium hypochlorite that can off-gas, in low flow rates. This is similar to introducing air bubbles in the line.
Ensure the suction line is clean and there is adequate NPSH. This is to prevent cavitations and consequent diaphragm failure.
Always use hydraulically balanced diaphragm metering pump. This is the only design which takes away the diaphragm stretching out of the equation as it balanced the process side pressure with the hydraulic pressure on the other side. It also ensures that the diaphragm lasts a very long time.