Use rehearsal marks foremost in places where the conductor will need to fix things – not necessarily always at the beginnings of sections. My rule of thumb is trouble spots/intricate textures first; changes of tempo, key, and meter second; and beginnings of sections last (these criteria often overlap, with two or even all three satisfied by one mark). If you’re not sure what a trouble spot looks like, then attend a few rehearsals and watch where the conductor has the orchestra start several times. If they are saying things like: “okay, start at…nine, ten, eleven, TWELVE bars before figure K,” that means the composer or engraver picked the wrong place for a mark.
In the example below from the second movement of my harp concerto, figure “F” is actually placed halfway through the episode – right before the brass starts a chorale in a lot of sharps. It’s a fairly delicate texture, with the strings adding touches of harmonic color, the cellos and bassoons pulsing, and the timpani providing a bridge between the two elements. The challenge for the conductor here will be to balance all those colors effectively under the harp solo. So the mark goes here instead of 8 bars back, or four bars forward on the upcoming tutti.
