Updating other people's plugins?

There's a lot of plugins that are 'dead', inactive or in some other way just basically doesn't work anymore. So, what if I want to update that plugin? (that's basically the idea of open source, huh? That other people can finish what one person starts).

What is the best way to update other people's plugins and release them to the public?

Let's assume that the source code is available on github (as a lot of plugins seems to be)
And let's assume that there is a devbukkit for the plugin (as plugins should have these days)

Should I fork the github repository? (If so, exactly how?) Should I contact the author and tell him what changes I have done and ask him to update?
Should I create a new page on dev.bukkit.org? Or should the original author update it?

 

Guidelines for Updating other user plugins

 

Thanks. Such a thread should be sticky in my opinion. Preferably with very specific information.