Dave Child has put together an excellent post on improving web site conversion rates. Well worth a read for anyone working in that area.
I would suggest a few more to that list:
11. Shorter ordering process means more sales.
Fits in with Dave’s idea of only asking information that is strictly necessary and saving time. The ordering process of an e-commerce web site is an area well worth some extra time and attention. Try to reduce the amount of work the user needs to do to the bare minumum, especially the number of page reloads they have to make. For each new page of the process you will have a percentage drop off the process (through boredom/changed minds/slow page loads etc.). Quick checkout means higher conversion.
You can see now why AJAX is so popular with modern e-commerce sites, it lets you create a process with no page re-loads and much of the user information pre-populated.
12. Remember every page on your site is a landing page
There’s still a lot of businesses who think users only enter their site through the index page and then politely work through the navigation – it just doesn’t work like that. In fact most of the time on e-commerce sites the user will land on the product page itself as these (should) be correctly titled with the product name itself.
Take a fresh look at each page of your site, as if that is the first and only page they have seen. Check your branding, message, call to action and navigation from that angle – you might be surprised.