
Search Engine Optimization, or SEO, is a topic that has entire web sites and books devoted to it, so I'm not going to try to cover it here. Instead, I'll outline the basic principals and how they apply to X-Cart. Disclaimer: I am not a Search Engine professional, but I have been working on the web for over 10 years and I do know what works and what doesn't. The information below is a basic overview only, there are many more factors involved and I always recommend hiring a Search Engine Professional to help you analyze your market and suggest the best approach for your specific store.
The Code
At the core of a well-optimized site is clean, optimized code. Out of the box, X-Cart doesn't do so well in this category, which is why we rewrote the templates from scratch. Our installation provides a clean framework for your content that puts the copy towards the top of the page and formats it in an optimal way (h1 tags for product titles, alt tags for images, etc). We have eliminated most of the tables, and gone with a CSS-based layout, which keeps all of the formatting in a central stylesheet instead of within the code of the site.
Another code item are specific tags that are extremely important to search engines. They are:
Title - this is the 'title' of a page, which appears as the link in the Search Engines, as well as the title of the browser
META Description - this is the blurb that appears beneath the link in the Search Engines
META Keywords - while not used much anymore, these are keywords separated by a comma (widget, red widget, red widgets)
All three of these tags need to be unique for each page.
Another very important piece of the puzzle is the URL of the pages in your site. By default, X-Carts urls look something like this: www.yoursite.com/home.php?cat=1. Search engines don't find any value in this, as there are no keywords in there and special characters (?=) are never good. Ideally, your urls should look something like this: www.yoursite.com/red-widgets.html. That not only gets the keywords into the url, but eliminates the special characters.
The best solution to customize the above tags/urls is to use a mod like CDSEO which we have used successfully on many sites.
The Content
Ranking well in the search engines is all about content, content, content. The more keyword-rich content you have, and the more often you add to it, the better the chance you will rank well for that specific keyword. I'm oversimplifying things greatly here, as search engine algorithms are extremely complex, but the number of times a keyword appears in your copy has a direct correlation with how you rank. For example, if you and your competitor are both selling red widgets, if you have 'red widget' in your copy 10 times and your competitor has it 5 times, Google will see your site as more relevant for the search term 'red widget'. Again, this is hugely over-simplifying things, but that is the general concept. Now the first thing most people ask when I say this is "Why don't I just write 'red widget' 100 times in really small text"? Well it isn't that simple, as that type of technique was abused over the years and it can now get you blacklisted from the search engines. The goal is to write copy with the customer in mind, so keep it readable. Keyword density is a factor of how often the keyword in question appears on a page, and generally the higher the number the better.
You also want to keep your content fresh by adding to it weekly if not daily. This can be achieved by adding new products, or by posting in a blog (a huge benefit for search engines). Many of my clients use blogs to post news about their industry, new products, etc.
Another thing to keep in mind with regards to copy is the dreaded 'duplicate content' issue. Essentially, Google doesn't like having multiple sites with the same copy in their search results, so when this happens, it tends to pick the one they feel is most relevant. An example of this is of particular relevance in e-commerce and that is when you use a manufacturer's description for your products. If a manufacturer has their products listed on their web site, and you are also selling those products, the manufacturer will almost always rank above you for that product's keyword, as they are the more relevant result. If your product description is exactly the same as the manufacturer's, chances are, Google won't list your site at all as it is a duplicate. To avoid this, you need to change the description enough so that it looks different - usually 25% different does the trick.
As far as X-Cart goes, you want to ensure that you have at least a paragraph of keyword-rich copy on every page - categories, products and most importantly, the home page.
Backlinks
Another important factor in how well you rank is how many sites are linking to yours - these are called 'backlinks'. If you have a lot of sites linking to yours, Google feels you are important, and they assign more weight to your search listings. This is also one of the most difficult parts of optimizing a site, as you don't want links from just anywhere. Backlinks should be relevant to your site - i.e. if you are selling 'red widgets' a backlink from the red widget association would be great, while a link from a site about the Red Sox isn't so great. You also don't want to get listed on 'link farms' or pages that are just lists of links. Ideally, your link should be within some relevant copy (like a blog post on red widgets), but a regular link on a relevant page will be good as well. The more important the page you are linked from is, the more value there is to that link. A link from Yahoo.com for example is much more valuable than a link from your buddy's blog.
Sitemap
There are two types of Sitemaps, one that is an actual page on your site and one that you supply to Google/Yahoo as a blueprint of your site. Both are essential. I recommend this software for maintaining your XML sitemap for Google. There is not currently a good sitemap add-on for X-Cart, as you don't want more than 75 or so links in your sitemap, and the current ones available list EVERYTHING on one page. Safetynetweb.com is coming out with a new sitemap mod shortly, so check with them often to see when it is available.