You can’t just stand there and expect to build muscle—not even when you’re lifting.
Before you begin a set of any standing exercise, place your feet flat on the floor and imagine you’re using your soles to tighten screws—your toes seemingly pushing outward and your heels straining to come inward.
Here’s the trick, though: You don’t want to actually move your feet. Just actively drive them downward and externally so they root into the floor and nothing can move them. If you do it right, the arches of your feet will become more pronounced and your glutes will tighten up immediately, which prepares your body for the lift. It also all but ensures that your knees will line up with your toes when you squat or deadlift.
Keep this tension in your feet throughout the whole set. The more you practice it, the more natural it will become and the more weight you’ll pile up on the bar.