A primary thing I would find out is who the client’s customers are. Are they middle-class housewives? Gen Y hipsters? If you don’t have an understanding of who the customers are then you will have a hard time designing a solution for them.
Once you know who the customers are, do some research. Interview people who are representative of the target customer. Capture emotive drivers… What do they think? What needs can the company fulfill? I usually create personas based on such interviews and ethnographic research, but you may not have that luxury or opportunity. Personas give you a empathetic target that you can use in design activities and it’s very affective.
That is the foundational stuff. When it comes to the project itself, you need to staff the right talents to support the goals. If it’s a site revamp and a revenue play, you’ll need a graphic designer and an interaction designer as well as a design lead (who optimally should be the person who did the aforementioned customer interviews).
The design lead should create an IA based on the domain of the site as well as the mental model of the customers when it comes to how they expect the site to work. This drives the site design and nav model.
When it comes to additional activities, you’ll need to look at user research to explore ideas around the new site, and usability testing to evaluate if users can accomplish the tasks you want/need them to do on the site. Design, test, refine. That’s basically it.