You may wonder what is entering metadata into Joomla! all about or if you have not prepared metadata, please take a look at the Writing great metadata recipe. When you're ready to go, read on.
The biggest mistake that clients make with regard to metadata is that they use site wide metadata. Joomla! even has a box where you can enter site wide meta descriptions and keywords.
The key to having highly effective metadata is to specifically tailor it to each and every page. It will then have precisely the right keywords for every article. Google will notice the continuity and your search rank for the page might improve because of it.
But even more important than this is your future readers/customers will ...