i've got 2 ways i throw it, im figuring out what i liek more:
1) Grip the ball like a four-seam fastball, put your index and middle finger together, and rotate them clockwise 45 degrees(1/8th turn) Then when you throw it, put pressure with your middle finger.
2)The seconf way is to grip the ball like a two-seamer, then take your finegrs and press them together, along the right seam. When you throw it, put pressure with your middle finger.
Both of these ways work, but use whatever works best.