When you link to your pages, your shopping cart items and categories, make sure that you use relevant keywords in your link text.
Don’t link just using text like “Click here to shop”. As an example, if you sell pillows, then better link text would be “Shop for pillows”. This tells the search engines that you think the target page is relevant to the words “shop” and “pillows”.
Secondly, for pages outside the shop, make sure the page name contains the keywords. If the url in your address bar looks something like www.yourstore.biz/page1.html that is not as effective as (following the pillow example) www.yourstore.biz/buy-pillows.html