Whiule not actually for "beginners" my understanding is that "the" definitive book on Applescript out there is Applescript 1-2-3, written by Sal Saghoian (product manager for automation at Apple for years) and Bill Cheeseman.
http://www.amazon.com/Apple-Training-Series-AppleScript-1-2-3/dp/0321149319

I never got the book myself. Back when I wanted to get it the latest version hadn't been published yet and I was waiting for it. Looks like its been out now for a while. Its supposed to be a great book for learning Applescript. I might pick it up myself to learn more about it. There are electronic versions of the book as well if you prefer that.

Edit: I just noticed it looks like this book hasn't been updated or republished since 2009, so its a little dated at this point. Applescript has changed a bit in the last 6 years, so not so sure anymore how good this book will be. Its probably still good for learning the basics, but for more current information, you might have to look elsewhere.

@Sobchak This site & the book offered there have been really helpful too me.

There is also an #applescript channel on the mac admins Slack channel.