How to improve Yahoo?
Stop making it the daily sport / OK! of the internet.
Quit with the massive flash ads
Quit with the obsession with z-list talentless celebs
Stop with pushing fad diets
Put email back to being email, and not some sort of spamvertisment mechanism
Search that actually works (and in email as well)
Reduce the number of pictures on the home page, it's like a 90's Geocities site (yes the irony isn't lost)
In other words, stop being the gutter press peddler of the internet and attempt to be a little more serious.