As my site gets bigger and sees more and more visitors I am trying to speed it up and streamline it.

So I used a PageRank website to see my score and I don't understand it's CSS request for me to "Use efficient CSS selectors"

This is part of what it tells me:

Very inefficient rules (good to fix on any page):
.commentlist .children li ul li Tag key with 4 descendant selectors
.nav * Universal key with descendant selector
ul.nav li.sfHover ul Tag key with 2 descendant selectors and Class overly qualified with tag and Class overly qualified with tag

If anyone can tell me what it is trying to get me to do and how to do it I would much appreciated.