The International Space Station (ISS) is maintained at an altitude between 330 KM and 410KM. So, at any point of time the distance of ISS from earth will be anywhere between 330 km and 410 km.
Because of its larger size and higer altitudes, one can locate ISS during dawn and dusk (morning and evening time) as the sun reflects light while it is dark on earth. ISS is third (after the Sun and the Moon) brightest object on the sky as seen from the Earth.
If you are eager to watch ISS, you can subscribe for timing alerts from NASA at the website: http://spotthestation.nasa.gov/