Describe the scenario. What is the population? What is the environment? What is the "problem" or question? What is evolving? What are the goals?
What is the "thing" that is evolving? Describe it's phenotype (the "expression" of its virtual DNA) and describe how you encode its genotype (the data itself) into an array or some other data structure.
What is the fitness function? How do you score each element of the population?
Are there any special considerations to mutation and crossover to consider or would the standard approaches work?