A mood, an effect

I prefer commencing with the consideration of an effect. Keeping originality always in view — for he is false to himself who ventures to dispense with so obvious and so easily attainable a source of interest — I say to myself, in the first place, "Of the innumerable effects, or impressions, of which the heart, the intellect, or (more generally) the soul is susceptible, what one shall I, on the present occasion, select?" Having chosen a novel, first, and secondly a vivid effect, I consider whether it can best be wrought by incident or tone — whether by ordinary incidents and peculiar tone, or the converse, or by peculiarity both of incident and tone — afterward looking about me (or rather within) for such combinations of event, or tone, as shall best aid me in the construction of the effect.

(Edgar Allan Poe: The Philosophy of Composition)

When I start a story, I do have a mood, which is hard to explain – a certain feeling, or an idea. Then when I write the story, I make every aspect of it relevant or appropriate to this mood – which would include landscape, architecture, [...] language, costumes, everything. [...] All the parts of the story should be consistent and in line with the mood, generating the mood, reinforcing the mood.

(Jack Vance: interview in Cosmopolis#42)