You'll need to open Map MFD and select ISS as the target, that will overlay the ISS orbital track onto the map. When the ISSbegins to pass over head (use the zoom), light the fires and head out. If the ISS is moving from SW to NE, leave out at approx. heading of 42 degrees, if it's moving from NW to SE it's about 138 degrees. You can tweak this while watching the Align Planes MFD after you've shallowed out your climb to build up escape velocity.
There is also Launch MFD, I use it every now and again, it gives you a crosshair to chase, it's not hard to use, read the docs.
I usually eyeball it watching MAP... Hope this helps, and happy orbiting!