Get rid of duplicate product URLS.

Thankfully Mike Smullin has already taken care of this with his easy tweak. Visit Mike’s post about this here. This requires one small modification to Magneto core, so hopefully someone will write an extension to take care of this without having to edit the core. Otherwise you will want to make sure you take care to make sure this isn’t overwritten during upgrades. In case the link above isn’t working, the modification is explained below.

Navigate to:
/app/code/core/Mage/Catalog/Model/Resource/Eav/Mysql4/Product/Collection.php

Locate:
->where('category_id=? OR category_id is NULL', $this->_urlRewriteCategory)

Change it to:
//->where('category_id=? OR category_id is NULL', $this->_urlRewriteCategory)

Make good use of robots directives to hide pages that will leak your pagerank.

There is a free extension from Yoast that will make this process very easy! You can view the extension here. Detailed instructions for using the extension (along with some other seo suggestions) can be found at the yoast website.

The Yoast extension will eliminate the indexing of pages that cause problems with search engines, while still allowing access to the good links on those pages.

I will add more as I find them, but these two resources will go a long way in getting your Magento installation ready to take advantage of good organic search results.