Welcome to the forum.
Blue smoke is usually engine oil burning white smoke is combustion temperature isn't high enough.
Does the glow plug light show when you turn the ignition on?
You could disconnect the coolant temperature sensor then see if it starts any easier that full force the glow plugs to be powered for 20 seconds. If it starts quicker then you need to investigate if the glow plugs are being powered from the glow plug relay and check the resistance of each glow plug they should be around 0.5-1.0 ohms each so you would need to invest in a multimeter if you don't have one.