Proper swing drill
What is the best way of ensuring the swing is on plane during the early part of the take away?
An easy way to check yourself would be to lay a club down in front of your feet parallel to your target line. As you take the club back, when the shaft of the club is parallel with the ground, it should also be parallel to club that's along your feet. If it is parallel to the club on the ground and parallel to your target line, you know the first part of your swing is on plane. Just remember to let your body move your hands into this position and NOT just by bending your wrists.