If you've been to one of my golf lessons, you would have probably heard me mention the importance of using a mirror when developing your technique. It's one of the best ways to see and feel what your golf swing is doing. When focusing on a particular movement in my swing, I would focus firstly at looking at the mirror whilst doing the swing move and then look down and swing the club trying to retain the same feeling. I would do this over and over again until I could feel the new movement.
This is the best solution to how to improve the technical aspects of your swing. I would mention the mirror the most when working on head movement and set-up positions. The most common fault in the swing when firstly trying to adopt the right swing is head movement. As mentioned above simply set-up in front of the mirror and put yourself in a state where you are about to swing the club back. This means place the club on the ground first. The biggest mistake when practicing in front of the mirror is not starting from the beginning of the swing with club on the ground. You need to treat every practice swing as if you're about to hit a shot.
Once you are set-up just look in the mirror and see your head stay in the same place in the backswing, then simulate the same feeling with your head when you look down and make a normal swing. Over time you will get very good at feeling what your body is doing.
Lastly if possible try and take the mirror to the range and set the mirror either in front of you or behind. It's such a great tool to use when practicing as you can see straight away whether your making the correct move.
If you'd like any further help in how to incorporate the mirror or other training aids just let me know.