
Chris B. answered 06/21/19
Highly Motivated Music Teacher Specializing in Percussion and Voice
One of my favorite techniques for practicing orchestration is taking pieces composed for soloists or chamber ensembles and rewriting for orchestra.
For example, try rewriting Beethoven's "Moonlight Sonata" (Piano Sonata No. 14) for orchestra. Spread out the left hand among the lower-sounding instruments, and pick an instrument to carry the melody through certain sections. Perhaps take Still's Miniatures for Woodwind Quintet and rewrite this for orchestra as well. This was the most common type of project we did in my college orchestration classes, and I find it worked very well to get the creative juices flowing.
Analyzing the piece beforehand definitely helps, just be very careful to accurately transpose for the non-concert pitch instruments, such as trumpet, clarinet, etc.