Here's how I whistle. Suck in your cheeks, like you're puckering for a kiss. Make sure the lips are a tad moist. Blow through the lip hole. It helps if you keep a tightness, or ambiture (sp?) which is how a horns or winds player would describe lip/cheek tightness. Inside, the tongue is resting against front teeth and a very light stream of abdominal air is supplying the whistle. Any luck?