If 100 people respond to your questions you'll probably get 100 different answers. Here are the general guidelines that I use:

1. Be comfortable. You need to be able to get in and out of the stance for hours if necessary. For example I can't have my left arm locked straight for very long without tension appearing in that elbow - so I keep it as straight as I can without locking it.

2. Have freedom of movement in your grip hand and arm. Whether you're pushing/pulling the cue during the stroke or just letting gravity do most of the work is not nearly as important, IMO, as making sure that your own body doesn't interfere with your cue's motion. I, for example, cannot play for any length of time with my head way down like a snooker player - it just causes too much tension in my right shoulder after a while.

3. Have your head over the cue and your eyes level wth the table. A lot of people will talk about finding your dominate eye then having that directly over the shot, but I've found that for me the proper position is with the right side of my nose over the cue. The main thing here is to be consistent. Shoot some long straight shots without paying attention to your alignment. When you've got the shot locked in pretty well have someone look at you and tell you what part of your head is directly over the cue.

4. Be balanced. I like to have my weight evenly distributed between both legs, so I end up bending both knees slightly instead of, say, bending my left knee and leaning forward from my straight right leg. I could jump straight in the air from my stance. Some people prefer a different weight distribution. I don't have hardly any weight on my bridge hand - just enough to keep it on the table.

5. Stand close enough to the cue-ball that you can follow-through without inducing any stress into your grip arm.

I do think that having your torso perpendicular to the line of the shot is a bad idea since that would make you lean over to the side to get your head over the stick, and then you'd have to crick our neck the other way to get your eyes level. But hey, I've seen some pretty good players with stances a lot stranger than that. Regarding Burt's advice, in The Deflection Tape he changes his tune a little bit about steering the stick. I'm still trying to figure out how it works at all - let alone as well as it does. And don't even get me started on half-ball hits making 90% of bank shots - it's like voodoo or something.