I bet it changes based on a few factors including age, prior mobility, etc. I do a few things at my current age:

  I wear Vibram "toe-shoes" so that my heel isn't lifted off the ground when I squat or do other movements and unless I'm lifting very heavy I go below parallel
  I warm up by doing either some prescribed warm-ups or by getting on the air bike/rowing for a few minutes + other warm-up activities
  I do the exact exercise movement I'm going to be doing if it's a movement like a snatch, clean and jerk, deadlift, squat, etc. to warm-up 

I don't do any stretching before or after. It's absolutely fascinating that so many different things work for so many people.