connect one wire to pin no 9 that is RESET pin second end of wire keep open. give circuit 5v supply then touch second end of wire to positive supply and remove. If you have a multimeter check voltage across pin no 40(Vcc) and 20(Gnd) is about 5V. Preset is one type of variable resistor that is used to adjaus contrast by changing voltage of pin no 3 of lcd. If you dont want to use preset then just ground pin no 3 of lcd. IF still your circuit dont work post picture of circuit you made.