Full Extension - Make sure that you get full extension with each of your strokes in order to maximize your efficientcy.
Proper Handfull - To make sure you get a full scoop of water, when you put your hand in the water, keep your arm straight and pull straight down.
Pull Through - Keep your elbow up and bend it pulling your scoop of water straight down the length of your body. Keeping your elbow up will engage the primary muscles in your back.
You can also do these drills to work on these techniques:
One Arm Drill - Using only one arm and a pull buoy, make your way down the length of the pool working on your technique. Then come back the other length using your other arm, again focusing on technique.
Front Sculling - Using a pull buoy, extend your arms out in front of you and scull with your hands to move you foward. This will allow you to get a feel for the water and practice getting scoops.