Alexander Zemlinsky gives a practical introduction to the way he rehearsed Erwartung (excerpted from Pult und Taktstock, March/April 1927 issue).
In my experience, the most difficult work is past when two artists, a singer and a conductor, convinced of the great value of this piece, devote themselves entirely to learning it until it is completely successful: the conductor, not burdened by any interests his boss might have, jokes along with the orchestra during rehearsals, and the singer, who – apart from having a beautiful voice (and the role absolutely must be sung beautifully) – must be capable of strong dramatic presentation. The most difficult hurdle is overcome when these requirements are met well enough. The orchestra part is not much more difficult than other modern works, and it has the advantage of virtually sounding “by itself,” so wonderfully is it scored.
I rehearsed the orchestra like this. I divided the players into very small groups, which I rehearsed separately; flutes and oboes: clarinet and bassoons: the horns alone: trumpets, trombones and percussion: first and second violins: violas, celli and contrabasses. Then all the strings and the harp: all the winds and percussion: and finally the whole orchestra without the singer. At that point, only two Sitzproben (rehearsals with the singer and orchestra) were sufficient before the actual stage rehearsals with orchestra began. Since the work lasts only a half an hour, much was accomplished during the usual three-hour rehearsals; it turned out that three such stage rehearsals were enough to achieve a thoroughly clear and impressive performance.
To alleviate certain intonation difficulties in the singing, I had a harmonium installed in a trapdoor located at a place onstage chiefly occupied by the singer, which occasionally cued her notes without disturbing the listeners in any way. Thus we managed a performance which betrayed not an iota of all its difficulties.