This post cover techniques to turn the board and adjust direction.
First it is important to understand the difference between a forward stroke and a steering stroke.
The forward stroke is used to propel yourself straight forward with minimal turning or yaw. The basics of the forward stroke are covered in Technique Post #3: Stacking the Shoulders.
The steering stroke is used to turn the board effectively. To turn the board, you want to use the angle of the blade and the stroke path to maximize turning. To go straight, you want to use the pitch and path to minimize steering. My friend Jeff Chang wrote a good post on his blog on using the path and pitch of the paddle: Paddle Steering by Jeff Chang.
To steer the board you basically want the blade to angle out away from the board at the beginning of the stroke, then follow a curved path as far out away from the board as possible, watch the video for a demonstration. The same applies to the backward strokes on the opposite side.
If you are paddling in a side or cross wind, you may have to use a slight steering stroke for every stroke just to go straight. Remember, the more forward you can get the blade towards the nose and the more you angle it away from the nose, the more effective the steering stroke will be. On longer racing boards you can also use the rail of the board to steer into the wind. Most racing boards with full rails will turn upwind if you put more weight on the downwind rail. Try taking the weight off the upwind rail, leaning the downwind rail into the water; this should result in the board turning upwind with less effort if combined with steering strokes on the downwind side.
During a race, you want to avoid paddling backwards and slowing down, so the crossbow turn and pivot turns are better options. Turns in a race can be very important and place changes often happen at turns, so practicing turns is an important part of race training. In Stand Up Surfing, turns can be even more important as a quick pivot turn can make the difference between pulling off a late drop into the bomb of the day and getting pounded.
Links to the paddle technique series posts:
Paddle Technique Part 0: Introduction to SUP
Paddle Technique Part 1: Choosing the Right Paddle
Paddle Technique Part 2: The Three Ingredients of a Powerful Stroke
Paddle Technique Part 3: Stacking the Shoulders
Paddle Technique Part 4: Reach and Catch
Paddle Technique Part 5: Recovery, Paddle Length and Grip
Paddle Technique Part 6: Turning the Board