Target your audience. You want to make sure that you know whom your audience is going to be geared towards. If it is toward a young, rich audience you can design your site so it fits a wider screen and lots of graphics for a higher speed connection. However you would not want to design that type of site for an audience that would be older or have smaller monitors and slower internet connection.
Accessibility is another important part of E-commerce. The thing about internet in general is that a wide variety of people can view any one website including those with disabilities. Alt tags and text links are good ways to make it more accessible along with being more searchable.
With all of today’s technology sometimes simplicity can be overlooked. Sometimes simplicity can be just as effective as a complex rollover image. Complexity can just cause confusion in navigation so keeping it simple can be more beneficial to the viewer. Also, while a splash page can get the viewer interested in your web site one that is too complex can take away form it too.