One of the best ways to continue to grow as an orchestrator is to study scores and analyze the use of orchestration. Through IMSLP and other websites, we now have access to countless orchestral and other large ensemble scores. Below are recommended questions to ask when studying scores for this purpose:
Sound -
Who is playing?
What choirs are involved?
How are the instruments used idiomatically?
What would be the equivalent texture if written for piano or another instrumental choir?
Harmony -
How is the harmony sustained?
Pedals?
Are there other means for creating resonance (like pizzicato, harp, or percussion)?
Melody -
Who is playing the main lines?
Are they doubled?
If so, in unison? In octaves?
Rhythm -
How does the texture accentuate the rhythmic structure?
What is the use of percussion or percussive effects?
Growth (and form) -
How does the orchestration clarify the form?
Do changes happen at important structural moments?
How are the dynamics orchestrated?