To be consistently competent in this daunting game, you need to swing on the correct plane throughout the swing. The goal really is to strike the ball in the sweet spot of the club every time. That affects how far it goes and where it goes more than anything. And that's what separates the pros from the amateurs more than anything. Of course what makes it a daunting game--perhaps the most daunting of them all--is to do just that consistently and effectively.
Well, I've got good news for you all. I've discovered a surefire way to start your swing on the currect plane and keep it there even if your concentration wanes if you tire during the round or on the range. Here's how it works.
As you address the ball (no, don't say, "Hello ball," as Ed Norton used to instruct Ralph Cramden on The Honeymooners--YouTube it), the shaft will form a particular angle to the ground. This will vary for different golfers. There is no ideal angle. The rest of the swing remains on that angle/plane, including the impact zone. Of course, keeping the head relatively steady and the forward arm straight helps maintain a measured, on plane swing.
As for swing speed, swing at a speed that insures you strike the club as close to the sweet spot as possible. That will allow the club to do what it was designed to do. For good pro models, watch Angel Cabrera, Lydia Ko, Nellie Korda, Ludvig Aberg, and Bernhard Langer.
One more thing: There's no need to overcock the wrists at the top of the backswing. Keep them relatively quiet ala Steve Stricker and Scottie Scheffler. With an on plane swing, they will deliver the coup d'grace automatically.