Personally I'd find someone in the city(if you live in a city) that's been doing graffiti for a while. Alot of graffiti artists around my city are always willing to meet with people who do graffiti or are trying to learn it. They will take you under their wing and help you create your own style and teach you the ways of the spray paint. Alot of them also will show you some good walls in the city to use as your canvas to learn on.