During the Renaissance, the five senses were understood to form a hierarchical system from the highest sense of vision down to touch. Vision was correlated to fire and light, hearing to air, smell to vapour, taste to water, and touch to earth.
Perhaps the human fascination with fire stems from the totality of its sensory stimulation. The fire gives a flickering and glowing light, ever moving, ever changing. It crackles and hisses and fills the room with the smells of smoke and wood and perhaps even food. It penetrates us with its warmth. Every sense is stimulated and all of their associated modes of perception, such as memory and an awareness of time, are also brought into play, focused on the one experience of the fire. Together they create such an intense feeling of reality, of the "here and nowness" of the moment, that the fire becomes completely captivating.
In all cases, a commonplace is a method of compiling knowledge for later use. In digital or analog form, this continued growth of stored ideas and projects is a key driver of intellectual development. Any time you decide to work on a project, you should attempt to collect and categorise all information that is relevant and useful.
Methodically noting and filing resources is a sign of a mature and deliberate craftsman—it is an investment into future learning and projects. Before long, you will begin to reach the point where this collection generates projects and ideas with minimal effort; previously isolated ideas are consolidated and curiousity spurred on.
Effective writing stems from intelligently connecting the dots between the concepts you understand and can articulate. It stands to reason, then, that in order to generate more creativity you must not only add to a knowledge base, but deepen and expand the number of connections within the totality of the network. By establishing and explicitly mapping your knowledge, you allow yourself the freedom to remix information. You will often find that solutions come from previously unsuspected fields or topics—proving to be analogous in some shape or form.
Richard Feynman was fond of giving the following advice on how to be a genius: You have to keep a dozen of your favorite problems constantly present in your mind, although by and large they will lay in a dormant state. Every time you hear or read a new trick or a new result, test it against each of your twelve problems to see whether it helps. Every once in a while there will be a hit, and people will say: ‘How did he do it? He must be a genius!’