Purchase good-quality art marker pens at a local arts and crafts store.
Place a blank sheet of thick scrap paper underneath the paper on which you are working to prevent the ink from bleeding through onto other sheets of your sketch pad.
Observe a range of samples of another artist's graffiti to see how she colors and shades her work. Look at street graffiti, borrow art books about graffiti from your local library or study any photos which you can find. Notice how some graffiti artists use only one bright color in the lettering while others create patterns of color within the graffiti lettering.
Choose a bold color or a combination of colors you would like to infuse into your graffiti design. Don't be tempted to choose too many colors as this will make your graffiti look too busy and will detract from the overall design.
Apply your strokes quickly, confidently and in one direction in the designated area. Keep within the outlines of the letters. Cover the entire area of your shape with color and don't leave any white patches of paper.
Apply a black outline around the letters to make the bold color within your graffiti letters prominent.
Apply other colors into your design using hues you think will work well together. Play around with the different ways you can create color contrasts within the framework of the graffiti letters. For example, apply one color to alternate letters or divide each letter so that one part of the letter is one color and the adjacent part is another color.
Draw some patterned lines within the letters and apply two or three colors to the design.