Draw out your graffiti letters... i used the curved line tool and the straight line tool for this. I zoomed inn X2 to ger the points on the D to look right.
Use the freeform select tool to move the letters on top of one another. Zooming in X2 can make it easier to avoid selecting part of another letter along with the one your moving by mistake.
Zoom in X6 and delete the overlapping lines.
Select the main colour and fill in your graffiti...
Press CTRL and A to select your picture, then copy it. Fill it all in with black, then paste your original image again. Make sure youve selected the bottom option that comes up below your toolbox, then move your coloured letters over your black ones so it looks like they have a shadow. ( i suck at explaining things)
Use white to add some pretty highlights and your done! =) this was my first tutorial, so i hope it doesnt suck too bad, but i figured that this place really needed some decent graffiti tuts! o.O