I have seen alot of posts like this, but not one that has this exact spot, so I'll put it up, this is only for horde and you need to be in Org for both ways (one low level way, and a higher level way)
Video quality is kind of bad, sorry for that
low levels
http://www.youtube.com/watch?v=LyHIEMCnWiw
this one is pretty simple, jus go find that guy called gamon and attack him with the desired weapon equipped
higher levels
http://www.youtube.com/watch?v=sjHBlwftzHQ
this one is a little more complicated but still pretty simple, find Cenarion Emissary Blackhoof in org, go to your reputation page (tab off of character page), and click cenarion circle, then click At War, and you can attack him to build up weapon skill, you might want to run because he is level 55 so he could kill some lower level characters, like he almost did to me