If you're launching an application using the "Run an Application" action, you can try its "Wait until launched application us started before continuing" option.
Other than that, you could try the "{WINDOWEXISTS:}" token, to see if the application has spawned its window.
However, neither will guarantee that an application is actually fully "loaded" in that it will properly process input; There is no method to check that within Windows, as far as I'm aware (as Windows has no way of knowing that a game, for example, has finished loading all its resources in the background).