All graffiti writers and artists are expected to have their own style. You won't stand any chance of making it in your pursuit to learn to graffiti if you aren't able to develop your own style. Your style should be as distinctive as your tag, and be aware that other graffiti writers are extremely protective of their own styles. Any kind of copying will not be tolerated.
When you're starting to learn to graffiti it is all right to learn by copying other writers style. But you need to use copying as a way to develop your own graffiti writing skills, not to create your own pieces. It is easier to learn to graffiti by copying a number of different graffiti artist's styles. This way you will find what parts of different styles you're better at and which parts you enjoy working with more. What you learn from other graffiti writers styles you can use to develop your own.
Only copy other writers' styles as you learn to graffiti. Don't use their styles. Learn to develop your own.
Once you have developed your own tag and graffiti style, you are ready to start creating your own pieces (short for masterpieces). It is important that each graffiti piece you put up is distinctive in your unique style and skill. While you learn to graffiti you need to focus on developing your skills with paint, markers, spray cans and other materials.
Because skill is just as important as style you need to work on your pieces until they're perfect. This is why graffiti writers have black books. They're used for sketches, copying down ideas and developing their pieces before they're actually thrown up. You need to make sure every detail is planned out in case you find yourself working in a time pressured situation. Every piece you put up is representative of you as a graffiti writer.
As you learn to graffiti put in place methods and techniques to ensure you create skillful and unique pieces.