> Squats, bench presses and deadlifts are extremely complex, high-risk lifts that serve no purpose for the average, non-competitive weightlifter.
You've clearly never had to lift a couch or push a car out of a ditch, even just squatted down to pick up something larger than a breadbox.
Your body isn't made of glass - it won't explode, and scaring people off these wonderful exercises is doing a disservice to humanity.
> Should they squat high bar or low bar?
Really whatever is more comfortable. High bar won't get you as much weight due to leverages but some people lack the mobility, or the desire, to low bar.
> Wide or narrow stance?
Totally based upon the individual anthropometry. If you have long femurs you can squat wider to get ride of some of that potential moment arm but that's going to load your hips to a greater extent. It'll also depending on how your femur hits your hip bone - I have to squat wider just to get my femurs into the right spot to hit parallel.
> Parallel or below parallel?
If you're competing, aim for just below -you're playing the game and you want 3 white lights with the most weight. If not, then do what your mobility / goals set. Far below is going to cause you to move less wait, but you don't want to be above to keep the knee strain low (note: your knees ain't going to explode, it's just not as nice on em)
> Flat shoes or heel lifts?
That's an ankle mobility question. If you can do it without, go for it, but many people won't be able to.
Stop living in fear of excellent exercises that get you stronger and build character. Progressive overload and months/years of experience will sort most people out before they explode into a pile of gooey chunks putting a bar on their back.
edit: put question marks at the end each quote to help delineate between question / response.