For those who have implemented an enterprise data management approach/strategy/plan, what are the most important steps/aspects you would advise someone who is planning to start?

To start with consider following aspects
1. Understand Business Goals and Objectives: Begin by understanding your organization's business goals and objectives. Effective data management should align with and support these goals.
2. Data Governance: Establish a robust data governance framework. Define roles and responsibilities, data ownership, data stewardship, and data policies. Ensure compliance with regulations and industry standards.
3. Data Inventory and Cataloging: Create an inventory of all data assets within the organization. Develop a data catalog that provides metadata and descriptions for each dataset. This helps in data discovery and understanding
4. Data Quality Management: Implement processes for data quality assessment, cleansing, and enrichment. Poor data quality can undermine the effectiveness of any data analytics initiative
5. Data Security and Privacy: Prioritise data security and privacy. Protect sensitive data, implement access controls, and adhere to data protection regulations.

1. Catalogue all existing types and sources of data within the organization.
2. Make the catalogue available to all consumers of data within the organization.
3. Document third party data sources, contracts, usability agreements, etc.
4. Interview end users of data throughout the org to understand how, when, where they use data in their work.
5. Identify/create a single POC for data in each operational team and have these folks engage in cross-functional communication and collaboration of data management
6. Develop a data literacy program for the org and raise the collective awareness of data management throughout
7. You MUST have executive level support and engagement to foster consistent data management from each functional area - encourage these leaders to add data management objectives to annual MBO's and KPI's
8. Develop a 3rd party data lifecycle model:  ID use cases, find data, calculate ROI, test the 3PD for effectiveness, contract the 3pd source, integrate the solution, measure/refine
9. Develop enterprise data management best practices: storage, retention, access, audits, etc.
10. You need a person (or team) whose sole job is enterprise data management - they come to work every day thinking about and managing the data
11. Create strong partnerships between the EDM (enterprise data management) team and the IT team - planning, architecting, etc. on data storage, access, BI tools, etc.

I'm sure there are more - but this is a good start.