If you have an automatic transmission, put it in neutral and start out real slow using brakes to keep the speed slow (this is especially important when on snow or ice). If you have a standard transmission, put it in low gear and use brakes just enough to keep your speed slow.
Never put your trans. in neutral, then you will over heat your brakes and end up with none.
@Headless Man: I respectfully disagree, especially if on very slippery roads. An automatic transmission will not slow the vehicle to much extent if it is a very steep hill (which I assumed the author is speaking of). Note that I said start out really slow and use the brakes to keep it slow. On very slippery roads, the transmission in gear will actually hinder your ability to brake and will cause sliding.... Now, if we're just talking about a standard grade on a regular road, I agree with you.