Request each instrument to play the melody line in exactly the same way. While this method does not provide for variety in the music, it does create a full, solid sound. This method is best used when the musicians are less experienced or the situation requires only a basic melody.
Play different instruments in the same scale, but a different octave. An octave consists of eight notes that make up each scale. For instance, the middle "C" note starts the C-major scale. The next "C" note on the music staff begins the next octave. Select some instruments to play the melody line in one octave and others to play either one octave above or one octave below. This creates a little more variety while keeping the melody line the same. This also works for playing in intervals of fourths or fifths, which keep the basic notes the same.
Use different instruments to play the melody in intervals of thirds instead of other intervals. This type of harmonization requires a little more work to figure out. When you go up or down a third, the melody will follow the same pattern, but it will sound and look different. To create a melodic third, go up two notes on the staff. For instance, if the note is a "C," move up to an "E." Pay attention to the flat and sharp notes in the scale and assign the appropriate flat or sharp to the required note. For instance, in the above example, if you are dealing with an "E" flat in the scale, you will be creating a minor third because you are not fully moving from white key to white key.