Research the graffiti styles that interest you. Take a walk in your neighborhood and observe the graffiti around you, especially if you live in an urban environment. Check blogs and image collections of graffiti you want to emulate.
Write a calligraphy-style word using a pencil. Make the word fatter by adding another dimension or outlining it with a paint pen. Practice your tag, drawing interweaving letters, a decorative picture and signature details. The consistency of individual flare is what makes graffiti true to its author.
Draw one of your graffiti words onto a paper bag. Using scissors, cut out the outline of the word leaving a word or image-shaped hole through both sides of the bag. Lay the stencil down wherever you want to spray your tag.
Shake your spray canister so the paint comes out evenly. Hold it about a foot from the surface and spray the paint over the outline. Avoid painting outside the bag.
Lift the bag from the surface and you'll have an even print of your original drawing.
Spray your paint against concrete or wood, guiding the nose of the canister from side to side with your arms and shoulder. At the same time, use your knees to go high and low instead of stretching your arms.
Fill in your basic design with heavier color. Paint with mixed media like charcoal and wheat paste if you want a grainier effect.
Outline in black or a darker color to make your letters and figures more bold.