Merry Christmas and Happy Hanukkah to those that celebrate!
When developing a program for a new client, my main goal is to create context through "filler" exercises. This often makes multi-joint movements much easier for them to understand. One of the simplest ways to get people to understand how to develop tension throughout the lower body is by creating awareness at the feet. Yes, your feet play a huge role in your training sessions.
As crazy as that sounds, the foot is arguably the most overlooked body part. When the foot doesn't actively contract during a heavy squat or deadlift, you're simply not maximizing your ability to utilize the muscles of the hip, knee, and ankle. Active foot stability gives you a much better opportunity to create as much force possible to move heavy weight.
To fix that, I implement single leg stability drills (no, not on a BOSU ball) in warm-ups and as correctives when necessary. These will not only help your squat and deadlift, but can also improve unilateral exercises, deceleration drills, and any other athletic endeavors you might have.
This progression is one I'll typically use for my athletes and/or people that display a great deal of congenital laxity ("hypermobility"). It's also a great progression/regression list to use for older individuals that are seeing their power and balance decline.
You'd be surprised how challenging these could actually be. If they're too difficult to start, I suggest just working on standing on one leg and holding for an allotted amount of time. Once that's easy, start working your way into the more dynamic stability drills above.