The eventual strategy should more or less correspond to the intended coverage of your review. Although you will need to aim for a satisfactory compromise between quantity and quality, the requirement for the search to be systematic means that you should err on the side of retrieval of too many items. You will find that having subject experts on your team judge the relevance of items once retrieved is more reliable than entrusting the review entirely to the vagaries of indexer subjectivity and inconsistency. Your search strategy will also include syntax that expresses the relationships between search terms. An information specialist can advise on these issues and validate the internal logic of your search statements.
Researchers often underestimate the time taken to develop an optimal search strategy.
You must judge the relevance of retrieved items to your topic. Check items that you already know of. Revision of the search strategy is thus an iterative process.