Create a series of chromatic chords with a view to constructing a storyboard for a tragic plot. Maybe this could lead on to a prelude or an overture for an opera. You will then need to have a micro-idea in your head of the opera, with all the important themes featured in the prelude or overture.
Give special attention to instrumentation or orchestration, rhythm and duration of notes depending on the plot.
Very often called an overture in this context. The term overture was used in connection with the term opera, so Wagner called his overtures preludes. The term prelude originally meant a work that was a preface to another.
There are two types of overture: