Unfortunately, there is not a simple answer to this question.
Data is the most important resource for any analytics project. Therefore, organisations need to capture as much business, transactional and customer data in a structured manner.
What we find works well is a data discovery workshop to understand the quantity and quality of the data you hold, where it is stored and what important business questions you would like answered.
Following the workshop, we can advise on the efficacy and suitability of the data.