a known segula is to recite the first 4 chapters of tehillim before going to sleep at night .its a famous segula , i hope it works !
another trick which i heard suggested by experts is not to be extremly nervous that youll have a nocturnal emiission, be calm if it happens ,it happens . but nervousness on the matter can itself cause the emmission.
i used to be plauged by nocturnal emmisions but as i got older it stopped as a joke once put it, (i hope it doesnt get censored ,and if it does,it does,) when your young you get wet dreams and dry gas emmissions (far**) when you get older you get dry dreams and wet gas emissions