Do your research. Browse graffiti books and the Internet to familiarize yourself with the many different types and styles of graffiti. Print or copy designs that appeal to you so you can draw inspiration from them as you work toward designing your own graffiti letters.
Draft your design. Draw a simple, stripped-down version of your words. Keep them basic at this stage. Focus on spacing out and sizing the letters correctly. You will need to leave some room between letters so you can build them up in a graffiti style later.
Develop your design. Once you have established a template you are happy with, you can begin to build on it. Experiment with different styles, drawing inspiration from your research as you begin build up your letters. Draw around the simple letters to fill in the gaps between them. Thicken the lines and overlap the letters in graffiti fashion. Take your time with this stage and draw as many different designs as you want. Use a pencil so you can erase any mistakes and edit your composition as you move along. It might be a good idea to work in a sketch book so you can collect your ideas and look back over the creative process.
Add detail to your graffiti words. At this point your graffiti words should be taking shape. All that is left is to add details. Many graffiti artists choose to add shading and highlights to their letters, make a mark on the page where the sun would be, before shading everything that would be in shadow. This can add a interesting 3-D feel to your design. Add other finishing touches you feel are necessary.
Practice in your sketch book. This will help you perfect your design and develop your drawing technique. Use it to keep track of any different ideas and look back on it to see how you have improved.