When cross-examining an unknown witness, you must observe the Motorcycle Rule. This is the rule that kept me alive through years of riding a motorcycle in Houston traffic (for a while, I had no usable car, and rode everywhere). The Motorcycle Rule, for those not familiar with it, is this:
They are all out to get you.
On a motorcycle, that means that you remain vigilant all of the time, and never assume that the other driver is going to do anything other than try to hit you. Pretending that the other driver is trying to hit you, you make it impossible for him to do so (or as near impossible as you can while still making your way to your destination.
In the courtroom, the Motorcycle Rule means the same thing: you make it as near impossible as you can for the witness to hurt you, while still telling your story to the jury.
An illustration: today I cross-examined a witness in my self-defense case. After the cross-examination, the court took a break and I visited with the detective. I told him that I had enjoyed it, and he said it was “interesting” and that he’d been looking for me to “open the door” to certain opinions he had — for me to give him reason to expand his testimony beyond that which he had been permitted to say on direct. I had followed the Motorcycle Rule, though, and had brought out my client’s story through the detective without opening the door giving him an opportunity to make things worse.
Until they demonstrate otherwise, they are all out to get you.