The first item on the agenda is to cut a tennis ball in half. Be very careful and use a sharp knife. I find a serrated knife is best for this project. Once the ball is cut in half you are ready. I know some golfers may be self conscious about using training aids on the practice range, so the drills I am going to show you could be done on the range, in your backyard (with plastic golf balls or no golf balls) or even in the house. The main thing is if you want to improve, you have to put in a little work daily!
The first drill is very simple and I call it the "gate" drill.
Use an alignment rod or golf club on your stance aimed at a specific target. Tee up your golf ball with an 8 iron, and sole your club behind the golf ball. Now place each half of the tennis ball about 1" on either side of your club head. You now have a gate for your club to pass through.
Remove the golf ball from the tee and I suggest you make some practice swings and see if you can swing the club head through the gate and clip your tee. If you successfully pass through the gate, then your path should be OK. For some reason our practice swings are always better than our real swings. Let's tee up a ball, use the 8 iron and see how you do.
I just love the focus this drill gives you. You can also check your divots with this drill. We want the divot to be in front of the tennis balls and not behind.
Now let's get a little more detailed with our path.
OVER THE TOP on the DOWNSWING
If your divots tend to point to the left of the target and they are deep, then you come over the top of the ball on your downswing. This means you are swinging too much from outside to inside on the downswing. We need to reconfigure the tennis balls. Place one half of the tennis ball in front of your golf ball about 6" and about 1" to the left. Place the other half of the tennis ball behind the ball about 6" and about 1" to the right. You will have a diagonal as pictured.
If your are coming over the top, you will more than likely strike all three balls (below)! Note below how my shoulders are aiming to the left prior to impact. The club head is going to follow your shoulder path leading to pulls, pull hooks and pull slices.
This could be caused by taking the club too far to the outside on the backswing. Make sure not to strike the outside ball on the backswing. This might be all the fix you need.
I recommend to follow the same procedure as the first drill. After you have your diagonal placed on the ground, start by making practice swings and see if can pass through the gate without striking either of the tennis ball halves. Once you have the feel, go ahead and tee up an 8 iron and begin hitting balls. If you tee the ball, you can leave the tennis balls in place, otherwise, every time you take a divot you will have to move the tennis balls.
If your divots tend to point to the right of the target or the divot begins behind the ball and you feel like you are scraping the ground through impact, you come too much from inside to out on your downswing. You will need to reconfigure the tennis balls. Place one half of the tennis ball about 6" in front of the golf ball and about 1" to the right. Place the other half of the tennis ball about 6" behind the golf ball and about 1" to the left. Your diagonal will look like this below.
If you are coming too much from the inside you would more than likely strike all three balls (below)! Note how my shoulders are pointed way to the right of my target prior to impact. My club head is again going to follow my shoulder path to right field causing the ball to start right of my target and I will hit pushes, push slices or push hooks.
This could be caused by taking the club too far to the inside on the backswing. Make sure to miss the inside ball on the backswing.
Both of these drills will help you identify if you have a faulty path and help you correct it! Remember you may have to make lot's of practice swings with the tennis balls in place before actually hitting golf balls.
Below is a comparison of downswings. The middle picture is the correct position prior to impact.