What is a one-sentence summary of the following article?
As with conventional and reverse swings, one side should be distinctly shiny, and the other side distinctly rough. Keep the ball as dry as possible. Grip it with your middle and index fingers on either side of the seam, with the ball resting on your thumb and third finger. The direction of the swing will be determined by the speed at which you throw.  At a low speed (under 70mph), the ball will swing toward the rough side.  At a high speed (over 70mph), the ball will swing toward the smooth side.  Note that the exact speed that determines the direction of the swing will vary based on the amount of wear on the ball.

Summary:
Use a ball with a prominent seam. Hold the ball along the seam. Bowl with the seam pointing straight down the pitch.