The first is financial . You will be spending money on your case, regardless of which kind of fee agreement you have with your lawyer. You need to have an idea of what you're going to spend on the case, and to do that you need to know exactly what must be done, what should be done, and what would be helpful but not critical . First, though, let's cover what you should do, since that at least is within your control. Some cases are quite straighforward and don't require much of an investment.
Most cases involving professionals, however, are complicated at the least and more often complex.
You need to know what the law is which will be applied to your case. Jury instructions, which are statements of the law, should be prepared at the beginning of the case, not before trial, so that you've covered all issues. It costs something to have your lawyer research and memorialize the research early in the case, but it's cheaper than missing an entire issue which will costs you much more in the long run. Don't be afraid to demand a full, legal analysis of your case, complete with citations. You probably have documents and other evidence helpful to your case.