A lot plays into account for vapor production. Mixture ratio of your liquids, higher VG content produces more vapor. Next would be resistance of your coil and type of attachment it is in, cartomizers and clearomizers, generally most tanks are not by design give thick thick clouds but a fair amount if the resistance is low on a set voltage device. Next element that affects vapor output is the ending wattage your coil is firing at, this is achieved several ways, coils resistance, lower the hotter it gets, Variable Voltage or Variable wattage devices most times can surpass a set voltage device as these can be bumped up in increments to produce more wattage at the coil. Last and final variable is air flow, adding in more cool humid air into the hot humid vapor coming off your coil in the end is one of the biggest factors overlooked, but a lot of times like with a clearomizer or cartomizer type attachment without major modifications you can't control this outside an adjustable air flow controller to open up an attachment to highly airy to very tight.
So pretty much you are left with affecting your coil resistance by either buying lower resistance coils or slowly adjusting up your Voltage/Wattage settings in increments, more advanced, rebuilding your coils yourself in the case of a Protank or such.