I used to think that all that was needed to write for orchestra, was finale. If you wrote a note out of range, it would tell you and you would be able to write the note in a lower octave, or in a different instrument.
While this is true to some extent, there’s an important piece of advice I would give fellow composers. It’s that you should get yourself a book on instrumentation. The one I have is published by Alfred. There’s things to know about instruments beyond their ability to play certain tones within the parameters of a given range.
On a piano, there are 88 keys and it is usually a preferred instrument for composers because the keys more or less sound the same, and the range is very well defined. It isn’t like a violin, which I remember learning in harmony class in college that the instrument actually prefers flats over sharps. On the piano, there’s no difference between a flat and g sharp. Or, to put it differently, those two notes will not sound different, they will sound exactly the same.
Let’s take a flute as an example for why a book on orchestration could be worthwhile. You might decide you want to write a solo for a flute that uses the lower register of the treble clef. There are some nice low notes, so why not. The problem is that in the orchestration book, it says the flute has trouble projecting anything lower than the d line, (just under the top f line in the treble clef) so it’s not going to be able to play out–read BE LOUD!–for this reason, a different instrument should probably do that, like some instrument from the string section.
So there’s range, and then there’s what each instrument can play loudly or confidently. And a lot of instrument specific peculiarities that you might not know, if it’s not your instrument or you don’t have a pro player to ask questions about it. So I say all of this to recommend this book, if you are a serious composer, I think it could help you a lot.