1. Plan Ahead
Singers have to plan ahead much like you would for big pieces like the B-Minor Mass or Missa Solemnis that require a lot of vocal stamina. But unlike those pieces, the Vigil has nothing to lean on—no orchestra players, no orchestral scores, no anything. It's all on you—the pitch, the excitement and the energy of the piece. So you have to pace yourself to make sure you are able to get through to the end.
2. Pay Attention to All Score Markings
Rachmaninoff was very meticulous in marking all the little things that he wanted the performers to do. If you listen to his piano compositions, you see how much nuance there is in his music and in his thinking. He knew exactly how he wanted his pieces to happen.
Dynamics make all the difference in the Vigil. Even if a crescendo is only for one beat, it is a big crescendo. But it's not the length of it that matters; it is what is supposed to happen emotionally. That happens throughout the whole work-going from fortissimo to pianissimo in the course of one measure, or even less. There is no place that he lets down.
To be constantly shifting up and down, up and down, is very difficult thing to do, even for a professional singer. Singing everything forte is easier than singing everything piano.
3. Watch Intonation
Maintaining good intonation is very difficult in this piece. The refrains and the key relationships in the various sections are very challenging. There are odd keys and odd key relationships, particularly in the "Magnificat." Also, the music crosses the passagio in the upper voices often and you have to move quickly from forte to piano and back again. All those little nuances take their toll on singers performing it.
For higher voices (tenors and sopranos), there is another challenge. The piece requires a great deal of light singing in the upper register, often followed by very loud passages in the same parts. Preparation, and ability to switch easily from light singing to heavy, is essential to maintaining your stamina.
My best advice is to always keep the voice in control. Knowing where you are in the piece and where you are going will help you keep the pitch and energy going through the entire piece.
4. Get Help with the Church Slavonic
The main problem with performing pieces from Russia or any of the Slavic countries in Eastern Europe are the languages—they are not languages that singers are steeped in. They can usually sing French, German, Latin, Italian, but not Slovenian, or Russian, or Church Slavonic.
Musica Russica has a pronunciation recording available as well as a good transliteration system. It also helps to have a vocal coach help the chorus with the language.
5. Directors: Allow Enough Rehearsal Time
One can take this piece for granted a little too much. It's not long but it is extremely dense. There is so much going on, between the study of the language and the musical challenges.
I've come into a couple of situations where there was not enough rehearsal time to get the piece in shape. One time I convinced the chorus to use the English version instead and that salvaged the performance.
In another case, it was unsalvageable. The conductor had to eliminate some movements, which was not completely satisfactory. So a word to the wise: Give the Vigil plenty of rehearsal time.