1. Open the game launcher
2. Click on "Options"
3. On the "Options" popup, check the box for "Disable on-demand patching"
The launcher should start downloading a 4GB patch. If it does not, exit and restart the launcher. After the patch finishes, play as you normally would.
Ever since I tried this I have not had a single server disconnection. Apparently what is happening is that the game downloads mini-patches while the client is playing the game...and especially when the client transitions from one zone to another. The constant patch installation along with game loading is enough to lag some clients out of the game. I believe they implemented it this way to avoid forcing every client to download a massive patch. IMO, the cost of endless disconnects and lag far outweighs the cost of waiting to download one huge patch.