There are many important steps, such as understanding of information design, Information architecture, interviewing SMEs, UI, and UX of product.
It is easy to assume that content is the only element users care about whenever they use documentation. But such an assumption is absolutely far from reality. Design is one of the most crucial elements of any online documentation. Visually-appealing documentation such as a user guide that contains relevant images and has appropriate videos embedded in it alongside with fonts and theme that aligns with the website design is always visually appealing to users and more user-friendly!
Maintenance of documentation is another key aspect to look after for a high DX. In case of updates, documentation should be updated too so that there is no lack of information for the users. These practices can ensure high adoption of APIs.