We've developed the first version of our website and going to lunch it and introduce it to a crowd. How do we know which part of our work has weakness and how we should correct it?
This is why you need goals for your website. Otherwise you don't know if it is working or not.
The goals should be about the website itself, not traffic to it. In other words, it can't be volume of visits etc., as that determines the success of your traffic generation efforts, not the website.
What are the actions people can take on your website? What do you want people to do? Most importantly: what is in it for them? What does a person get back for spending time on your website?
Track activities (the more visitor-centric the better) such as clicks on buttons, paper/info downloads, newsletter subscriptions, etc. The more you have to offer the client, the better tracking you will get.