you might like your coffee strong, but please trust me on this; if you take the finest coffee in the world & make it too strong the delicate, unique flavours that you have gone to so much trouble to acquire will disappear & it will taste like a heavy caramel concoction.
so if you are looking for a starting point, and perhaps it is slightly on the weak side but at least it is an unambiguous measure, i would suggest 3 level desert spoons of freshly ground coffee beans with the isomac grinder set to position 6 (i.e. with the '6' at the front of the grinder) for a cup that will hold 250mL of water.
obviously a finer grind means you need less coffee & vice-versa for a coarser grind.
hope this helps. if you are having trouble, please call & we'll try & sort it out over the phone