Your first touch, set the direction by holding down and move left to right. Then "flick" by doing exactly that...just grazing the surface like you were flicking some dust off the screen. When the ball is in motion, you can also control the way the ball moves by swiping left / right.
You nailed it - that is exaclty how you control the ball. The first flick you set your players position on the lane. I wish you could change your mind and move him/her if you want to, but you can't. If you don't flick perfectly straight up and down the ball will go on an angle as well. I wish they'd use 300 Bowl's shooting mechanics with flick bowling's graphics.