Understanding arranging for orchestra / strings / etc.

I love love love what Spitfire Audio has given us with all these great labs and the BBC orchestra, as well as all the paid-for offerings. Now, how best to put them to practice? I started by listening to Beatles tunes and picking apart what George Martin created for them for accompaniments. Listening is always a good place to start, right? But now I'm wondering, are there youtubes or coursera or other resources (books what are those?) people recommend to gain a general approach, what to do, and more specifically what not to do, in terms of arranging for orchestra, strings, brass, and the like? I have nothing but time.