Before analyzing sales data in Excel, the first and most important step is to clean the data and remove duplicates. This ensures that the analysis is accurate and not affected by errors or repeated entries. Cleaning the data also involves checking for and correcting any errors, managing missing data, and ensuring that the dataset is well-organized with consistent data types for each column. Only after this preparation should you proceed with steps like applying filters, creating pivot tables, or visualizing the data with charts. This foundational step sets a strong base for reliable and meaningful analysis of sales data in Excel.