Hey Chris,
AppleScript is not like other languages – unfortunately Apple did a lousy job of moving it forward after its initial development, so applications can have wildly different syntactic requirements. That means you have to learn each app separately. There is significant overlap of course, but it's a challenge – especially without owning a copy of Script Debugger
There is now a Lite [free] version of Script Debugger available – the full version demo reverts to Lite mode if not purchased in 30 days or so.
JXA and AppleScriptObjC have hit the scene, so there are many more tools available than there used to be – but that makes for even more studying...
Introduction to AppleScript Language Guide
Learning & Using AppleScript & JavaScript for Automation (JXA)
Learning and Developing AppleScripts
Join the Script Debugger Forum. It's the single best place for AppleScript help these days.
There's also:
and
Applescript Users List Archive (search with Google site search)
I haven't touched this for some time, so it's more than a little bit out of date:
BBEdit is a good app to learn with and has the additional benefit of being one of the best programming editors for the Mac.
(The commercial version reverts to “Lite” after a demo period but is still waay powerful and scriptable.)
There are some decent books, but they tend to be better references than learning tools.
I could go on, but I'll stop here.
-Chris