A lot of my students have trouble getting the club all the way to the top of their swing while keeping their lead arm firm.
This tends to happen because golfers aren't rotating properly and are using all-arms to get the club to the top of the golf swing, breaking down the lead arm.
A great way to find the correct feel for the top of the golf swing is to raise the club and rest it on your shoulders, properly rotate your hips so your back is to the target, push your arms away from your body, and swing.
This will help teach your body the proper way to rotate, which won't only get rid of that 'all-arms' swing, but will help you generate more power from the lower half.
Easy Drill to help students feel how the body should be moving and how it should look in the back swing. Will help activate the body and silence the arms or the need to lift with the arms. This drill can be sed for any golf level and is especially good for juniors and beginners. I like to do this drill sometimes before I go out and play if I do not have time to warm up on the range. Gets the body ready to do the job.