I had a chance to study with very good musicians. One of them was my orchestration teacher. He taught me to pay more attention to instrumentation and orchestration.
Through him I again discovered the art of Nikolay Rimsky-Korsakov (couple of year ago I visited his home – now a museum, – in Saint-Petersburg, sensed a very nice atmosphere there). Korsakov was one of the greatest orchestrators and used to say that the secret of a great melody is hidden in how it is orchestrated. So putting emphasis on orchestration rather than composition.
Henceforth, I reserve some extra time to spend on thinking about a specialty of an instrument (-s) I am writing for. If there are more than one, then I think
– how would be better to mix them,
– what would sound great together and
– what would sound great if they have to play separately (one at a time – solo),
– how to melt their notes together,
– how to put in nice layers,
– how to cover with each other,
– how to support each other,
– how to show contrast and differences they have etc.
Often it pays off, if you check that important aspect.