Book:
Apart from the Applescript 1 2 3 book you mentioned, there are also a few more books for beginner:
AppleScript The Comprehensive Guide to Scripting and Automation on Mac OS X
https://www.apress.com/us/book/9781430253525
AppleScript The Definitive Guide
http://shop.oreilly.com/product/9780596102111.do
There are also a few simple and short guide to get your feet wet:
AppleScript Finder Guide (Free)
https://applescriptlibrary.files.wordpress.com/2013/11/applescript-finder-guide.pdf
Inside Macintosh- Interapplication Communication (Free) - bit more advance and detail but you would understand better about apple events and there's a chapter on applescript too
https://books.googhttp://macosxautomation.com/training/video/peachpit.html
Apple developer guide: (If you wanna find out what has been changed since 2009, this is the site!)
https://developer.apple.com/library/archive/documentation/AppleScript/Conceptual/AppleScriptLangGuide/introduction/ASLR_intro.html
All of these are old, but honestly speaking, not much improvement were made....and I still strongly recommend the Applescript 1 2 3 book since it's for beginner!
Video tutorial serve as an introduction to applescript by the author of Applescript 1 2 3:
AppleScript Seminar:
https://www.macosxautomation.com/applescript/video/moovs/AppleScriptSeminar.mp4
Forum/community you should join: (Ben Waldie does a lot of tutorial on applescript, you should check him out)
http://macosxautomation.com/training/video/peachpit.html
Applescript User Digest: (sign up for this and you will get updates on user requesting help for applescripts):
https://lists.apple.com/mailman/listinfo/applescript-users
There are plenty of videos on youtube and except "applescript", your searching keywords would be "Sal Soghoian" and "Ben Waldie"
Though Sal Soghoian no longer works as the product manger for Apple automation, he is now working for The Omni Group, so it's worth checking out those scripting tutorial from The Omni Group apps too.
In my opinion, I would rather learn Javascript since that's what apple is heading to, check out JXA, it's very stable and you have the opportunity to master a widely used language. Unlike the moody applescripts, giving you trouble once a while after an update on mac os / specific application update, eg: no longer supporting applescripts.
Hope it helps!