You just use the scope the same as always. If you're using it right, with both eyes open, it isn't hard to see the crosshair with the eye looking through the scope and the target with the other eye. The target will be out of focus through the scope, but not with the other eye, and the only thing you're seeing through the scope is the crosshair which will be in focus.
It is easier with scopes on the lower magnifications such as 1-3X, but not impossible even with more magnification.