Sentence:  First I make <WSD>preliminary</WSD> watercolor sketches in quarter scale ( approximately * * f inches ) in which I pay particular attention to the design principles of three simple values - the lightest light , the middle tone , and the darkest dark - by reducing the forms of my subject to these large patterns . 
Meaning of the word marked with <WSD> tags:  denoting an action or event preceding or in preparation for something more important; designed to orient or acquaint with a situation before proceeding