I have used a Holga at times and there is really no special trick to handholding. All I can think is that you are either accidentally double exposing the film or you have a defective shutter. The first two look a lot like double exposures, the last one less so. Double exposures are very easy with Holgas since the winding and shutter mechanisms are not connected. However, if everything is like this, I don't know why that would be happening.
To test it, you can take the back off, press the camera closely to your face, click the shutter and see what it does during exposure. You should see one quick flash of light, if you are seeing two distinct flashes of light when you do this, it would seem like a shutter problem. The Holga shutter is so simple, I don't know how it would do something like this, but who knows?