Choose the genre of music for the instrumental. While the first choice may be new age, jazz or classical, consider other popular genres like rock or country. Any genre of music can support an instrumental.
Select a style for the instrumental. Not every instrumental needs to be calm and soothing. There can be hard rock, driving blues or melodic country instrumentals. The style can then be slow, moderate, fast-paced, thematic or contrapuntal.
Compose the piece of music so a single instrument is the voice. The instrument will then carry it throughout the piece. Or, the composer can have several instruments take turns between musical phrases. Use the keyboard as the controller for the computer.
Master the composition by running it through "filters" in the software. They can quantize the notes so the music is steady and even and also automatically adjust the levels so that the music has an even dynamic throughout.