It depends for me as well. The main two things I will try are changing balls, or slowing down my speed just a bit. It's really just a feel thing, depending on how the ball is reacting, and what type of pattern it is. If I feel the ball is rolling out a bit, and losing energy it will definitely be a ball change. If I think it may be more because the ball is coming through the breakpoint a bit slow, and coming into the pocket behind the head pin a bit, it will probably be stay with the same ball, and slow the speed down just a bit, and maybe move in a board if I have to. I've talked to some very good bowlers who are firm believers in moving up or back a bit on the approach because that is less likely to change your line to the pocket, but that has never really worked for me that well. The bottom line is you want to make sure you're using a ball that is saving as much energy as possible, and still get you to the pocket, from there you have your adjustments options narrowed down a bit.