In all javascript of Mapviewer, you will have to define a center point and the zoom level. It's two important settings in order to have a beautiful rendering.
Example of javascript :
var mapCenterLon = -122.45;
var mapCenterLat = 37.6706;
mapview.setCenter(mpoint);
mapview.setZoomLevel(mapZoom);
var mapZoom = 0;
When you create a map tile layer, you have to give the coordinate system. If you gave the good informations during its creation, the zoom level definition is automatically fill with good values.
Example for the Netherlands :
The best way that I have found is to play with MapBuilder because in the render windows you will retrieve this information.