If you're looking to improve the overall length of your swing you're looking to have this nice long back swing a great drill that you can use is the counting drill. Now this drill is excellent for performing its task so making sure you have the time to complete the back swing one thing which is in the not great for in the short term is hitting consistent golf shots.
Longer Swing Golf Drills - The Counting Drill (Video) - Lesson by PGA Pro Peter Finch