There are a number of different approaches to maturity assessments. It also depends on the structure of your organisation and what you would like to asses, but I have some recommendations from recent experience conducting data management maturity assessments for Services Australia.
We used the CMMI Data Management Maturity Model. I found this was the most comprehensive and logical assessment out there - with much lower level of detail explaining each criteria. You can use this model to do a self assessment by interviewing SMEs and recording results in excel. I found it was useful to map the categories to functions and expected completion dates. It’s about $100 for the model and not too much more for an enterprise licence. It has been well worth it for me!
Other models have been developed by Gartner and other experts, but didn’t quite work for our organisation. It’s also common for consultants to conduct assessments.
I found the self-assessment the best way to really understand your strategy and sequencing.
We conducted assessments on Data Management, Data Quality, Metadata, and Data Management Platforms - and are just about to finish the whole array of assessments covered in the model. I’d be happy to share my experiences if you have any questions.