Prepare for a concert with new music for a minimum of 1 week. If you have experience with the music, you can cut this down to 2 to 3 weeks.
Practice your music daily before the performance. Schedule your practice songs for different days. If you will be singing three songs, practice one song each day in preparation.
Schedule one day per week to sing every song in the concert from memory. Memorize the songs early, so that you do not risk forgetting the words or music during the concert.
Meet with other performers at least once per week to go through the entire concert. Most problems in a concert occur because of poor communication among performers. Prevent this with practice.
Sing a vocal warm-up exercise of your choice in the morning. One good exercise is starting with the sound "hmm" and singing down a perfect fifth from a comfortable pitch. Continue this exercise by moving up a minor second each time. Find the highest pitch in your range and begin a fifth below that pitch.
Buzz your lips on the first five notes of a C-major scale. Choose the octave that best fits your range. Ascend and descend up to G and back to C; then move up a minor second to C#. Continue this exercise until you reach a G-major scale.
Drink warm tea with honey. The honey helps to loosen phlegm and lubricate your vocal cords. The tea warms your body and prepares it for singing.
Avoid singing the concert music before going on stage. At this point, you will either know the music or not; concentrate instead on warming your voice and preparing mentally.