This is not a tutorial on the double lift, there are a lot of sources for that already. Instead this is a look at how lay people turn over a card compared to how magicians turn over a card.
I recorded a number of lay people, asking them to turn over the top card and place it back on top of the deck. Those recordings are below.
What is interesting is most of them pulled the top card backwards with the fingers of the palm down right hand, and grasping the card between the thumb and finger tips, rotated the card end for end. Rarely did anyone flip the card over from the side.
Magicians, on the other hand, usually will perform a hit style double lift, turning the card(s) over sideways. That is the way I usually do it as well. Below is a video showing some different performers (Tommy Wonder, Daryl, Harry Lorayne and others) doing double lifts.
As an exercise I played around with doing a double lift turning the cards as a layperson does. See the practice video below. A couple of things I discovered… While lay people slide the card backwards before gripping it, you can’t do that when doing a double. You need to first grip the cards. I found that starting with a get-ready break lets you hold the ends of the cards against the right thumb as the fingers slide over the cards (not moving them) until the fingers and thumb have control of the double. As this is done, if the left hand moves slightly forward it creates the illusion of the card being pulled back.
Also, when turning the cards, you need to keep them aligned with pressure between the left little finger and the base of the thumb.
While this is how lay people turn over a card I still prefer the hit style of double lift. It seems more fluid.

Really interesting. I love the video of laypeople turning over a card.