First of all, we do not encourage any illegal activity so please ensure you have permission to spray before you start.We suggest practising throw-ups before you try a full piece, just to get used to the spraycan. Don't go over anyone's work (throwies may go over tags though); only spray on surfaces that are free and legal to spray.
Make sure the surface is dry; if possible use a roller with white or your.ctml to get a good undercoat first. Start with a skinny cap to make the outline first.Don't make it too prominent e.g. use beige or grey on a white background.This is so mistakes can be easily fixed.You may prefer to use a different colour for each letter or character so they can be distinguished more easily but that's up to you.
Don't feel you have to stick to your sketch - it's just a guide and you should modify as you see fit along the way. Keep stepping back from the piece and checking it's all in proportion, don't stay too close all the time.