Do I Need to Cross Examine the Witness?
If they didn't hurt you (especially with experts), then why give them a chance on cross? If you can get the information in with a friendly witness, why not?
What Part(s) of Your Case Did the Witness Undermine?
Before standing up and starting, determine what key areas you need to address. Remember, this isn't a deposition! Giving yourself a little "warm up" wastes time and dilutes the impact of cross.
Is There Prior Testimony From the Witness (like a deposition)?
If you have prior testimony, did they contradict the testimony in any significant ways? If you are going to cross a witness (especially an expert) with prior testimony, make sure you have clear impeachment. It seems that the impact in trial is always a bit less than we trial lawyers think it is going to be. Don't over use this tactic as you could quickly bore the jury (or judge) if not making big points.
What, if any, Exhibits Need to be Covered on Cross Examination?
If it can go wrong, assume it will in trial
No Open Ended Questions - Keep Them to Yes or No as Much as Possible.
Do not ask why? EVER. Make the questions clear that they are "yes" or "no". If they are fighting with you, try to enlist the assistance of the Court. Or, before you begin, set it up for everyone in the room that "Sir, I am going to ask you a few yes or no questions, okay? If you cannot answer yes or no, would you let us know and I will rephrase the question" (or something like that).
If it isn't going well, do not be afraid to just cut it short or stop entirely. If it's not going well, it will likely get worse (unless that is part of the plan and you haven't used your big guns yet)!