Others have clearly defined the steps that need to be taken, and the order in which to take them. For me, the greatest challenge in marketing online is building the first fold on the home page. If your visitor scrolls down or clicks off into the site, you have a potential customer. In fact you have one who is likely to grant you a little slack. Thus perfection is not demanded throughout the site.
Top quality is sufficient.
But the first fold must be absolutely perfect. Think of a newspaper. The top fold of the first page. It's what shows in vending machines and on newsstands. Many, that's certain.