To begin with, I would examine the conversion funnel. This means analyzing the visitor's path from the moment they arrive on the website until they complete a purchase. I would review data on where visitors drop off at each stage of the conversion process from previous years to identify any significant inconsistencies. Important metrics to consider would include bounce rate, exit rate, and the time spent on the site. Next, I would assess any modifications made to the site over the past year, such as updates to design, user interface, new features, or changes in the checkout process. Significant alterations could impact conversion rates. I would also take into account external influences, like competition and market trends. An increase in competition or shifts in consumer shopping behaviors could affect the conversion rates. Finally, I would analyze customer feedback or reviews for any recurring negative themes. This feedback can provide valuable insights into areas of the site that may be contributing to a decline in conversion rates.