I believe there are 5 keys to having a good golf swing.
Great set up – address position
Correct swing plane/path of club
Correct Body movement
Every golf instruction book always includes a section of getting into the correct position at address because it is ABSOLUTELY CRITICAL TO HAVING A GOOD GOLF SWING. I cannot emphasise enough how important a good set up at address is. Most golf pros can predict a golfers handicap and CONSISTENT ball flight will be before a golfer even makes a swing just by looking at how they set up to the ball. I recently took a short break from playing golf and went and seen a fellow professional for a lesson. The first thing he worked on was just tweaking my address position so I could make a better turn.
A great place to work on this is in front of a mirror so you can see what you are doing.