I'll add to this list from time to time, as I think of other items.
Many of my observations and arranging insights came from this great book, and it's highly recommended for anyone who writes for big bands. (Click the image to visit Amazon.com)
It's great to be creative and fresh, but it's a waste of time to re-invent the wheel. So, if you study some of the most popular arranging methods, you'll know "what to look for" when transcribing, and will have a larger "toolbox" when composing and arranging your own work. Here are some notes I made while studying "Inside The Score", which I hope you'll find useful.
Since I know that many of the people who visit this site will be familiar with the Buddy Rich chart of "Ya Gotta Try", that might be a good place to begin. (There are multiple recordings of this on my Buddy Rich - Live! page.) Sammy Nestico's techniques are undeniably-good, so have fun exploring this brilliant arranger's work...