As a Project Manager, before I start to even think about Web Design, I need to understand the websites overall purpose. Understanding and achieving the goals of a website ultimately determines whether or not I have done my job successfully.
I would say that 99% of all websites are built to fullfill a need. In almost all cases it is to fullfill a need for information. There are all types of information out there on the web, everything from 100% factual to 100% false. Your site may have information that users want to find, or it may contain information that you want users to know, but they don't necessarily want to. It is very important to understand all of a sites needs. The user may want information, but you may want to sell them something. Bottom line is that behind all of these needs are goals that determine our behaviors. It is the goals that drive users to websites and to make purchases.
Determining your user's goal initially is what will make or break your website. If a user's goal is not fullfilled by your site, they will simply click off your site and be on to the next one in seconds flat. Goal-oriented design is the process of creating solutions that empower people to achieve realistic goals. All goals are important, but you may not be able to deliver them all, and you certainly can't design for every possibility. If a web project is going to succeed, you need to know which goals to shoot for.
The first step that you can take in determining your websites goals is to start writing down what needs to happen for your primary users to reach their goals? You can also write down what your site must avoid to prevent failure? Another good way to start to get a clear picture of the full range of goals a site needs to fulfil is to consider all the people or groups who have some significant interest in the project's success.
Once a sites inital goals are set in place, web designers can now begin develop a web site design that has those goals at the core. The utimate goal of your website should never be an after-thought!