I've had several clients new to lifting lately and I've seen a striking similarity between "used to lift"ers and "brand new to lift"ing. Here's the similarity:
The brain and body doesn't know what it means to move. "Move through your hips" means nothing to a person who doesn't have the mind-muscle connection to actually move through the hips. "Squeeze your shoulder blades together" usually results in someone shrugging their shoulders to their ears -- they moved through their blades, but doesn't know how to squeeze them together.
Here are three ways to build a better mind muscle connection with your muscles.
TIME UNDER TENSION (eccentric ((lengthening of muscle))
The longer you take to slowly put your body in to position, the more your brain will connect with the tissues making the movement happen.
In the squat for example, if you were to just let gravity bring your body down in to the squat, the body's natural mechanics will happen passively, rather than actively. We want the body to be ACTIVE through the movement.
In lifting for sport, this is crucial to help people understand how to LOAD and BRACE the body. If you haven't taught your body to properly load at light weight, how will your body feel when you've got 400 pounds on your back and you just drop in to your squat? Odds are not great you'll automatically be tight to drive up out of the bottom. You're more likely to lose tension in your hamstrings, your hip flexors, spinal erectors.
TIME UNDER TENSION (concentric (tightening of muscle))
The longer you take in driving out of the position, your body will likewise feel muscle, core function, and balance issues it didn't otherwise notice. Slowing down the push also keeps the body in a better position when the move is over.
Take the squat for example. The same muscles that leveraged you DOWN in to the squat are going to be the same ones the body uses to leverage you OUT of the squat. Taking time in this DRIVE phase will also increase the neurological connection of the brain to those muscles (it was also likely burn a whole bunch -- which is fine ya big baby).
Say you're new to squatting and you have a great slow DOWN motion, but then drive up real quick so that the weight shifts, your feet move, and you're over extended through your lumbar spine. You wouldn't want to immediately go in to your next squat. You'd have to adjust back to your stance. So taking your time when you're new will help you recognize these subtle changes.
ISOMETRIC (Iso holds)
Another great way to make the body aware of what muscles SHOULD and SHOULD NOT be moving is to squeeze (contract) or release (eccentric) the muscle in isolation. I'm a fan of "ISO holds" because the body can focus on the single muscle that is supposed to move and you consciously know what your "hip flexor" feels like.
Here are three examples of isometrics.
The static leg raise which turns on the hip flexor. In a seated position, drive one knee toward the ceiling for 10 to 20 seconds.
Glute bridge which extends the hip. Most people often conflate moving through their hip (squeezing glutes and pushing pelvis forward) with moving through their spine. By locking your abs and spine in place, you can better feel exactly what a glute contraction should feel like (at the top of a deadlift or squat or on a push press).
Finally, there is an isometric hold of a dynamic movement. For this, you hold certain points of a movement to force the body to maintain proper position, mechanics, and neurological connection. In the squat, holding the "bottom" position really forces the hip flexors, quads, and hamstrings to fire the entire time in that leveraged position.