This is a helpful little tip to reduce your latency that I learned a year ago from the famous warrior Swifty:
(With warcraft exited and not running)
1. Click on start, run, then "cmd". In the window that just opened type "ipconfig" and press enter.
2 You'll see something like "IP Adress . . . . . . . .: [Your Ip here]
3. Write down the Ip address.
4. Next, Click on start again, run "regedit".
5. The Registry Editor will show up, Open "HKey_LOCAL_MACHINE", "system", "CurrentControlSet" , "Services", "Tcpip" , "Parameters". "Interfaces"
6. Now in interfaces look in each folder until you see the one with your IP address.
7. Right click(anywhere on the white area of the tab), New, D-Word Value, Name it "TcpAckFrequency". Double Click it. Put "1" as a value and press Ok.
8. Close the regedit. Now disable your connection, enable it and finally login to the game.
My connection dropped from 180ms to 33ms using this trick. You can see your latency by mousing over the little computer monitor icon which leads you to the game menu on your hotbar. MS stands for milliseconds, and is really the time it takes you to send information to wow and then get something back.
This will surely help anyone lagging in areas like Ogrimmar, Ironforge, and dalaran which will in turn allow you to sell your goods in the more frequented major cities..
Let me know if it helps in the comments section.