Depending if the site has already been built and is going through a redesign VS building a brand new site is very different processes.

Joe points out some critical starting point questions thaty you should have clear answers for in order for you to design with the user in mind.

SITE DESIGN
Much of what we're talking about is building UI design from usability and information architecture methodologies to create the site.

SITE PERFORMANCE OPTIMIZATION
The next step to optimization is to look at site performance and determining if there are areas of improvement which can improve your funnel or optimize your sales and test for varying designs (based on your hypothesis) and use analytics to answer your questions.

MARKETING OPTIMIZATION
Lastly, it's looking into the marketing optimizations where you evaluate marketing ROI, testing of landing pages, and evaluate various marketing channels.

Experts above all offer great information on what to pay attention to. But as mentioned, without details, we are all just making assumptions.

Feel free to schedule a call to discuss further.