It is more and more common these days that most elite and tour players do a lot of golf specific training in the gym. Doing a golf swing properly involves movements that is unlike other sports. The most important movements to practice at the gym is maintaining spine angle whilst rotating through impact.
The exercise that I use most commonly in the gym involves using cable cords. I firstly face the mirror and go into my golf posture. I then hold the cord in my right hand and practice having the right hand start at the top of my swing. I then pull down and rotate my body whilst still having my right wrist hinged back just as I would if I was going to hit a ball. What I'm looking for also is seeing my head stay in the same position right up until impact with my body rotating.
I then grip the cord in my left hand and start the motion at the same point at the top of the backswing. I pull down with my left hand this time keeping a bow in my left wrist right up until impact just as I would with a normal swing. This is a perfect exercise to strengthen the left hand and arm as this needs to be the dominant arm for a right handed action.
The other view that I like to have when using the cable cord is having the mirror side on. This angle is where I can see the angle of my spine. I do the same two exercises with both hands. This time I'm very interested in seeing my spine angle stay the same right up until impact while rotating. I'm also trying to make sure I see my left glute at impact. This means that I'm rotating the correct amount through the ball.
If trying theses exercises, you will start seeing vast improvements in your game. Also one last point is that put the resistance at 2 or 3 kilos.
If you need any further help in discovering the right golf exercises for you, just book in for a session.