A main key to throwing strikes is to make sure that your direction is towards home plate. In other words, you want to be in line to your target (the catcher), and the stride is what starts it all.
The stride should be directly towards the catcher while not opening up your shoulders, hips or feet too early. You should feel like the underside of your front foot is pointing towards the target. Try to land fully on your front foot or on the ball of your foot.
To practice this, set your back foot on the rubber to simulate where you will push off. Then draw a straight line from the center of your foot towards the center of home plate. Go through the full windup and take your stride, pausing when your foot lands. You’ll want to land on, or very close to, that line.
Go through your motion a few times without throwing a pitch and then transition into delivering the ball. Each time, monitor where your foot is landing and how direct your stride is towards the catcher and home plate. You can also practice this out of the stretch. The line is a good way to make quick corrections if you are too open or closed in your stride.
You can draw a line in the dirt or use a string to be aware of your direction in a bullpen setting. You’ll get used to knowing the importance of direction and landing in the same place every time. This can lead to more strikes, more outs and, ultimately, more wins.