STEP-BY-STEP ANSWER:
Step 1: Identify individual preferences and utility functions for all members of society.
Step 2: Choose an appropriate form of the social welfare function that reflects the desired balance between efficiency and equity.
Step 3: Aggregate the individual utilities using the chosen function, which may involve summing or weighting individual utilities based on fairness criteria.
Step 4: Apply optimization techniques to the social welfare function to determine the allocation of resources that maximizes overall welfare.
Final Answer: A social welfare function is constructed by systematically combining individual utilities into one function which, when optimized, provides the best resource allocation in terms of both total utility and fairness.