lets see-i have 10 yrs of experience orchestrating...hmmm
Buy all of these books:
http://www.amazon.com/Essential-Diction ... hestrationhttp://www.amazon.com/Orchestration-Dov ... pd_sim_b_7http://www.amazon.com/Workbook-Study-Or ... tion+adlerstart with those and then begin orchestrating
Also if you can't play a wind instrument- you should learn one before starting because without that experience OR reading hundreds of scores you have no idea what kind of things instruments do and play in the real world
Trumpets don't play long borning notes all day- they ususally do articulated stuff on off beats or cool runs followed by fanfares
French horns pretty much play 4 note chords on off beats teh entire time with sometimes taking the lead... but there's pretty much an entire class you need to take on how to write out those 4 notes to come out well written with perper counterpoint and no parellelism
anyway get to reading
also- a bad way to start is a book with the word TABLATURE on it
The pocketguide to orchestration above is the best book i own and have ever read on the subject but you have to read the other stuff first
enjoy learning about the ranges of the SERPENT and SACBUT (they're instruments) in the Forysth book