Write the alphabet in bubble letters. This is the starting point for most graffiti writers. Try different looks with the letters until you find a look that you're comfortable with. Perfect your favorite look and make it your own style.
Write bubble words. Use the letters you perfected and put together words. Many graffiti artists use their names for practice. When you write the words, overlap the letters and try writing letters of different sizes to get a more fluid look.
Draw simple objects -- things you see every day -- in bubble form. You can draw animals, cars, your breakfast or any other thing, as long as you emphasize bubbling and stay away from straight lines and sharp edges.
Add color to your drawings. Color, as well as effective shading, can add depth to your images. The shading separates objects in front from objects that are behind, so the image appears to pop out from the surface on which it's drawn or painted. Bright colors add to the popping effect.