The forward stroke is the most important thing you do when you're paddling. It's what you do most often. First of all, the power in your stroke comes from a torso rotation, not really from your arms. The muscles of your back and your torso are much bigger muscle groups than the muscle groups in your arms, so make use of those to give you forward power. I do that by straightening my arms and using a framework with straight arms and my shoulders, with my arms stretched out from my body.
So imagine you've got a huge beach ball tucked into this space, or you've got a dead fish hanging from the paddle shaft in the middle that you want to keep well away from your nose. That's the sort of position you need to adopt. Paddle goes in, close to the front of the kayak, as far forward as you can reach in an upright position. The torso provides the power to drive the stroke.
You exit the stroke when this arm wants to bend. You'll feel that it's coming through to about here and then you've got to do something with it. You've got to bend it. That's about the position where your paddle is roughly 45 degrees to the water. If you carry on, putting power on your stroke beyond that point, you're going to be lifting water and that doesn't drive you forwards. What you're trying to do is plant the paddle and pull the boat past it. If the paddle starts to move, your energy is misplaced.
So paddling into the water close to the kayak, drive with your torso through fairly straight arms, top arm is in a pushing mode, bottom arm is in a pulling mode. Lift out when this arm wants to bend, place the paddle in on the other side for the next stroke. That's the upper body part that you can normally see when someone is paddling, but there's a big component of your power that comes really from inside the kayak.
There are more components involved in the Kayak Forward Stroke. Nigel has used this brief segment to provide tips focusing on the upper body part that you can normally see when someone is paddling.