in addition to Melanie, turn off all power that goes to your external device..pot and blah blah. Also, use voltage regulator with the lowest quiescent current need. Regular 7805 are not appropriate. 78L05 are better but there's a bunch of more efficient.

12F683 is a good choice if you need PWM and ADC. The POT command is not appropriate to read from a POT when your PIC have internal ADC. Should use ADCIN instead. 12f675 will also do the job if your skip the PWM to a home-made sound procedure.