One of the best ways to improve your impact is with the aid of an alignment stick. A very common impact position that I see most golfers in, is where the hands tend to stay behind the club head during impact rather than the hands staying in front. This will often cause 'thin' and 'fat' shots as you will tend to hit high on the ball instead of compressing the ball into the ground.
This drill is an awkward drill but very effective. What you do is take an alignment stick and place it in your left hand if you're a right hander while you're gripping the club. Use a SW for this drill as you won't be able to take the club back very far holding the stick. Ensure half the stick is gripped by the hands and the other half is left of your left hip.
The idea now is to take half swings with your SW with the stick and through impact making sure the stick doesn't hit your body but stays left of your left hip. If you achieve this it will mean that you're pushing your hands forward through impact instead of 'flipping' up. It is recommended that you place yourself on video while doing this so that you can see the improvements.
It is amazing how many times I've placed people on the video whilst doing this drill and see the improved position. Obviously once you have done a number of swings with the stick, try and then simulate without the stick and see if you can have the same feeling and same results.
If you'd like to ask any questions about impact or would like to book a lesson, just let me know.