When you put your hand in a flowing stream, you touch the last that has gone before and the first of what is still to come - Leonardo da Vinci

Practice must always be founded on sound theory.

The reader, at one look over this page, immediately perceives it full of different characters; but he cannot at the same moment distinguish each letter, much less can he comprehend their meaning. He must consider it word by word, and line by line, if he be desirous of forming a just notion of these characters. In like manner, if we wish to ascend to the top of an edifice, we must be content to advance step by step, otherwise we shall never be able to attain it.

A young man, who has a natural inclination to the study of this art, I would advise to act thus: In order to acquire the true notion of the form of things, he must begin by studying the parts which compose them, and not pass to a second till he has well stored his memory, and sufficiently practised the first; otherwise he loses his time, and will most certainly protract his studies. And let him remember to acquire accuracy before he attempts quickness.

Take a piece of glass of the size of a half sheet of royal folio paper, and fix it... between your eye and the object you wish to portray. Then move it away until your eye is two-thirds of a braccio away from the piece of glass, and fasten your head by means of an instrument in such a way as to prevent any movement of it whatsoever. Then close or cover up one eye, and with a brush or a piece of red chalk finely ground mark out on the glass what is visible beyond it; afterwards, copy it by tracing on paper from the glass, then prick it out upon paper of a better quality and paint it if you so desire, paying special attention to the aerial perspective.