Sketch out some ideas for your graffiti sign using a set of colored pens and paper. Work through some different designs and practice reproducing your motif on paper. There's little room for error once you start painting your piece for real. If this is your first stab at graffiti, stick to something simple.
Change into your old clothes and pack your spray cans and completed design in a bag. If you plan to create your graffiti in an area with poor natural light or at night, pack a powerful torch or other source of light.
Find a large area of wall where you can paint your graffiti design. Make sure you have the permission of the owner of the wall you plan to work on. Spraying graffiti on private or public property is a felony in most states if the damage you cause rises above a certain level.
Lay your design on the ground and start to recreate it on the wall. Be prepared to alter your design. Spraying graffiti onto a vertical surface is very different from drawing on a piece of paper so it's likely you'll make some mistakes when you first start out.
Sign your finished design with your name.