A confirmation review of the safety plan is required during compliance assessment with ISO 26262. Its production could be facilitated by creating a specification of the standard’s requirements in FCL (Formal Contract Logic), which is a language that can be used to automatically checking compliance. However, we have learned, via previous experiences, that interpreting ISO 26262 requirements and specifying them in FCL is complex. Thus, we perform a formalization-oriented pre-processing of ISO 26262 to find effective ways to proceed with this task. In this paper, we present the lessons learned from this pre-processing which includes the identification of the essential normative parts to be formalized, the identification of SCP (Safety Compliance Patterns) and its subsequent documentation as templates, and the definition of a methodological guideline to facilitate the formalization of normative clauses. Finally, we illustrate the defined methodology by formalizing ISO 26262 part 3 and discuss our findings.