One great practice for both learning orchestration and learning composition (they are connected you know) is taking an existing piece of music for piano and experimenting with orchestration.
For a little fun, I took an original piano composition by my friend Rob Kovacs and did an orchestration.I am posting on here so you can here the both the similarities and the new affects created by the orchestration.
First is Rob’s original composition for solo piano. (composed for a 24 hour film festival in which all film makers have 24 hours to make a short film)
Then the orchestration I added