Zen Cart has many SEO features already built into it however lots more SEO needs to be done to help your store get good rankings, attract visitors and begin making sales.
Here's what I did for better Google Search engine results, i suggest making a checklist first:
1.) Make a list of the search terms you want optimized. These are all the words and phrases a potential customer would enter on a search to describe what you are selling.
2.) Your web zen cart site pages needs to contain these search words within the text. Google will scan your web zen cart site and create a concentration list.
3.) Very Important IMHO, in your admin, make your category names include your most important terms. And use the plurals and singulars if possible. This shows google your terms are an important part of your zen cart site.
4.) Still in the admin, for each category, and then additionally for each product, click on the circular meta tag link and add the appropriate terms and phrases to each. The top two fields on the meta tag page are the most important. Information given in the meta tags will be used to give info when your listing appears in google. Basically, for some products i used the singular forms, some i used the plural and some i used both, just to make them a little different.
5.) Next, you need to update the file that google uses to show your web zen cart site Title.
Change/update the file includes/languages/English/meta_tags.PHP.
This allows you to add more search terms to the tagline and they won't be seen by the user but google will still recognize it. Notice again how i integrated the plurals between the two lines yet when you see them on google, most of it is hidden so it doesn't look like were just throwing out tons of words and phrases.
save this file and upload to includes/languages/english/YOURCUSTOMFOLDER/meta_tags.php to create an override file to preserve this info when you do an update.
6.) Edit home page description and keywords meta tags
These tags are also included in meta_tags.php. The description is the small blurb the search engines provide visitors searching for your products. Create an attractive description that gets visitors to take action on your zen cart site.
Even though the keywords meta tags does not have much significance these days, include it anyway by adding approximately 10 keywords separated by commas or spaces.
7.) You need to create links to your zen cart site, both incoming and outgoing. if you have no links google doesn't think you're very important. the incoming links are more important than the outgoing, but you need to be connected to other zen cart sites .
8.) If you have completely updated your zen cart site and have included all of your SEO search terms, now you need to make a zen cart sitemap so the search engines can easily index your zen cart site. this is a map of your zen cart site so the search engines know what your zen cart site contains.