keep your eye on the ball把眼睛放在球上，说明这时需要专心一点，所以这个表达引申为了小心谨慎地行动；警惕；谨慎小心。

【例句】
You have to keep your eye on the ball in business.
做生意必须时刻小心谨慎。

In this business if you want to be successful, you need to keep your eye on the ball.
如果你想在这份生意上成功，你需要集中注意力。