If you follow the course of ...

If you follow the course of one man through constant practice, your intelligence would have to be crude indeed for you not to get some nourishment from it.
 Cennino Cennini

Quotes from the same author

Now then, you of noble mind, who love this profession, come at once to art and accept these precepts: enthusiasm , reverence, obedience, and perseverance. As soon as you can, place yourself under the guidance of a master, and remain with him as long as possible.
 Cennino Cennini
If thou shouldst paint mountains in a good style and to look natural, take some large stones full of cracks and copy them.
 Cennino Cennini
If you set out to copy after one master today and after one tomorrow, you will not acquire the style of either one or the other, and you will inevitably become fantastic, because each style will fatigue your mind.
 Cennino Cennini