You mean start a application remotely and have it appear on the box you ssh in to?
if so then you run
from the target box, then just ssh in and set the display to ":0.0"
If you mean you want to run an application from a remote system, and have it appear on your system, so you control it remotely, then you don't set the display to myip:0.0 or use xhost, you just ssh in with
the display will automatically be set. Then you can start an app from a remote location, and have to appear on the box you are logged in to.