You hear the term “ball-striker” from pro golf broadcast analysts and frankly, it is a somewhat meaningless phrase to most golfers.
In essence, it is the ability to hit the golf ball on the geometric centre of the clubface. But why is that important? Well, the basic premise is that any strike of a golf ball off-center (towards the heel or toe) will result in twisting of the clubface. The result is less ball speed and distance, and even worse, a clubface that ends up open or closed to what you intended. (Plus, it does not feel great)
You can also hit a golf ball too high or low on the face, but that is usually less disastrous than horizontal errors, so for now let’s focus on those.
An easy way to improve your ability to hit more shots in the center of the club face only requires a place to hit a ball (real ones or soft practice ones) and couple of coins. You can do this indoors or outdoors.
Place a coin outside the toe and heel of your clubhead at address, leaving enough room for the head to pass by. Start with slightly more room between the coins and clubhead; you can tighten it as you progress the drill.
Try to hit ten full swing shots without touching the coins. If you can do this, tighten up the gate that you have created with the coins and continue.
Practice this drill every time you have a practice session over the off-season and by the team your golfing year begins your ball striking should be on-point.