The inner game of Orchestration.
First:
Read Berlioz’s book –but with his own examples not Strauss.
For a general study any recent orchestration book will do.
If you want to know about today’s general outlook about the whys and wherefores read Adam Carse’s book. Mr. Carse gives you all the orchestrational old wifes tales; Brahms bad, Wagner good, the French, bizarre etc. etc. It never occurs to him that orchestrating for opera might be different then for symphony. Or that a tone-poem, being a hybrid form, has more in common with opera than symphony.
The rhetoric of orchestral writing is different than others genres.
First compare how accompaniments are notated (orchestrated) in the piano sonatas, string quartets and symphonies, by the same composers. Mozart for example frequently uses Alberti bass in his piano sonatas but very infrequently, if ever in his symphonies. Also examine different musical eras to see the changes in instrument techniques.
Consider the differences between heterophany and doubling. Especially true if you are interested in spectral composition. Some times one must construct discreet parts out of contrapuntal lines to create fullness and texture. This is also a good way to avoid the hard edge caused by too many unison doublings.
Instruments and their Persona:
The use and techniques of instruments have changed over time but what remains is this:
Instruments also represent persona–a trumpet is not just an instrument but also a character that plays a role of trumpet in the orchestra. The trumpet is always in the lead and is always a solo even when it does harmony. For the trumpet, as in all the instruments, you can orchestrate for type or against type but the “type” is there no matter what. All players and instruments have a slightly different history and a tradition. Learn this. Would a first violin naturally be more musically assertive than a second violin or a viola? OK, before I feed you too many stereotypes that might be wrong remember –these are things you must discover on your own through listening and study so you can develop your own approach.
Register can have a strong effect on an instruments persona. Extreme notes on any instrument change its character and its strength. The flute can be more pervasive as it get higher in pitch, not the oboe. Some instruments have more than one persona. The piano, for example, is the instrument with the most persona, it can accompany, be a soloist, or blend with other instruments in many different ways. I will discuss the laptop a little later.