Typically speaking, cross examination is an effort to develop testimony that supports your theory of the case or makes specific points you believe are important.

The idea is to ask specific questions that you know the witness will have to answer a particular way. Leading questions allow you to guide the witness where you want to go. Direct questions are open-ended and often allow the witness to explain things in greater detail.

It's all strategy, but I can assure you asking direct questions on cross-examination isn't a good approach. But you're absolutely right--Rule #1 is to be sure not to ask questions if you don't already know how the witness will answer.