basically get some brushes ( ask people how to do this im too tired to tut) and then make a layer, make a few blak strokes with the brush set, get different set, make new layer and brush white with that set...... use a brush no more than once, preferably only 2 brushes form one set , then change to keep it livened up.... layer black/white untill you like, sometimes i get 5 layers sometimes i get 15. just play around wif them, dont forget to fade them in if they get too bright and out-standing coloured..... blend my frend, blend