The items below need to be done to any Magento site before or immediately after go-live.
Some of them take a lot of time but will return a lot of value for your client.
System Settings - please check these:
Go to: System - Configuration – Catalogue set the following:
This will fix the problem of multiple entries for products that appear in multiple categories.
The result will be that this canonical meta tag appears, which you can see if you view page source htML: <link rel="canonical" href="http://yoursite/TheProductName" />
Important: Once you have saved these settings you need to reindex your data. Go to System - Index Management and run reindex data).
Prevent HTML improvements message in G. Web Master Tools – Prevent pages with same name, title message
Update (Oct 2016)
Under HTML Head:
NB: NOW add Title and Descriptions page by page
1 - CMS Pages for each page in CMS pages
Check that there is a default site map called sitemap.xml – Place this in the root.
ALWAYS do a careful scan through the entries in your site map! Check for duplicates or similar URL’s that can be produced. Be a detective and look for parameters like search and sort which can make a single product page point to a number of duplicate pages.
Of course you WILL remember to submit your sitemap to Google Webmaster Tools!
Always add logo alt tag.