Here are some instructions that give the ratio of salt-to-ice and other such details. I've never tried them, so try, experiement, and let me know how to improve it!
There is also a disk style version of this machine (I don't remember the brand, though). Rather than use a bucket (which takes up a lot of space in your freezer) this uses a disk that fits on the bottom of a plastic bucket in which you churn the ice cream. The version of this that I saw, however, did a poor job of freezing the mix (i.e., it couldn't get it cold enough to freeze more than a slush). That's based on only one batch of ice cream, so your milage may vary.