In addition to your customers, take advantage of technology to improve usability. For instance, log files tell you which pages are most visited and for how long, unique vs. repeat visitors, etc. They will not tell you whether users found what they wanted, or why they abandoned their shopping carts.
Many services advise on predictable problems such as broken links, missing ALT tags for images, page load performance, but are as anticipated unable to spot complex things like difficulty in locating products, awkward navigation, meaningless graphics, or poor results from on site search.
Flow
It is important to create a uniform feel for your website. Uniform doesnt mean boring, rather it mean consistent. When a visitor lands on your homepage your goal is to engage the user. As the user browses through the site, a uniform feel is going to simplify the user experience. One of the worst web sites make every page look wildly different, so the visitor never becomes comfortable with the site. If you make your web pages utterly different, it is less likely that your visitor becomes quickly familiar with the site.
Images
There is nothing more boring than a...