Artistic vision is one aspect of creativity. Like any other talent there are some who seem born with a gift for it and others who need to be, not so much taught, as exposed to, a way of seeing and thinking. I think if you are motivated to express something you find a way to express it. How well you express it has to do with your innate or learned talent as well as technical skill in execution..
Artistic vision has elements of brainstorming and free association. The greater your awareness of your surroundings and openness to new ideas, the greater will be the creativity unleashed. Awareness is the raw material. Everything you see, hear, taste, smell, and touch, everything you experience, can be revised, expanded, turned inside out and upside down, combined with other things, edited, stripped, recolored, resized, etc, etc, ad infinitum.
Sometimes the idea is conscious, that is, you are focusing on trying to create or invent something new or focused on observing what’s there. Other times it just hits you in a flash of inspiration. For example, the artist who did the tree log colored pencils on the Street Art Utopia website may have seen a bunch of sticks tossed on the ground and it reminded him of pencils. He took that as the nucleus of the vision and turned it around in his head and played with it until he came up with something that satisfied him. Or he may have had a commission to do a large outdoor installation and whatever his feelings and thoughts prompted him to create could have been a conglomerate of textures and colors he was drawn to at the time. It could have been a theme that interested him.
Proportion, texture , color, and good composition can be learned. They have to do with aesthetic values and principles. Vision can be nurtured and enhanced. A more sensitive way of seeing can be learned. But some of it has to come from what is inside of you and the kind of person that you are. In a certain way it is your personality made visible. It has to come from what you are drawn to. It has to do with being fully present, seeing, hearing and absorbing. It has to do with first having the awareness and then being sensitive to it’s deeper associations and meaning whether it be it’s humor, or the beauty and poignance of it’s utter randomness as in found art, or surrealistic juxtapositions. It can even be the beauty in it’s utter ugliness, which then is no longer ugly!!