It’s a highly subjective question, so here’s a highly subjective answer.
- Who is the website intended for? If the website already exists, what kinds of users does it already have, if any?
- What information exactly needs to be communicated to these users for the website’s function to be considered successful?
- Are the intended users or the message likely to change in the future, and if so at what rate and degree?
- What are your motivations for working on the UI?
- In particular, how do your motivations differ from the those of the intended users? How do they differ from those of anyone else working on other aspects of the site?
- What is your budget for the work at hand, in terms of both money and time?
- Do you have the freedom to try unconventional solutions, or are standard ones more appropriate to the context?
- Who owns the UI once you have “finished” working on it? Will others need to change it independently?
- How closely coupled is working on the UI to taking into account and understanding technical limitations of implementation on both the back end and the front end?
- Have you eaten a solid breakfast this morning before beginning?