There are many different types of golf swing faults and golf training aids can go a long way in helping any golfer deal with their specific problem area.
The golf swing is the essence of the golf game and therefore it would not be a bad idea to get even two golf training aids that are specific to your swing fault.
The golf training aid that I have found to be very effective is the weighted club. This is a very golf-specific golf training aid as you go through the exact same motions you do with an ordinary club but with more weight. This greatly helps in strengthening and conditioning all the relevant muscles.
The inside approach is another great golf training aid to help improve any golf swing. This particular device is extremely useful for slicers and helps deal with this problem fairly quickly.
Another golf training aid is exercise tubing, which is very affordable and yet very effective. The strength of this device is in its ability to break down the golf swing into as many different phases as you would like to focus on for the sake of improvements. It offers specific resistance training for each phase.
A stability ball is a golf training aid than any golfer with a bad back should have. There are almost countless different stretch exercises that you can with it. And what makes this golf training aid even more attractive is the fact that you can do your exercises in the office or at home when you have a moment.
A simple pair of dumbbells can be a golf training aid that is very useful to any golfer. They are usually very portable and there are many exercises that can be done with hand weights.
Use of a golf training aids all boils down to the golfer knowing exactly what they are doing when using it.