Let me star off by saying I am by NO means a designer. I'm interested in learning AS3, and was wondering what some of the best books/resources there are out there for an absolute beginner.
This depends a lot on your background. Do you have programming experience from other languages/platforms?
Although i haven't read them myself, Colin Moock's Essential Actionscript 2/3 are supposed to be good books for getting started. Other than that there are a lot of amazing resources online (Google ;)). For RSS feeds check out feeds.adobe.com
Other than this i think the same tips & tricks apply to actionscript as to any other programming language. Practice makes perfect ;)
This may sound strange but I recommend the free documentation provided by Adobe called Programming ActionScript 3.0 (PDF). That's how I learned AS3.
There are some O'Reilly books as well as books by Colin Moock which you may want to check out.
Adobe's live documentation is a good searchable reference and they have a programming book (PDF) as well. OSFlash is a good community site with open source code and tutorials you can look at. Haxe is a great alternative language and compiler with extra features. To see some nice graphics examples with source code, check out Andre Michelle's laboratory.
Right now, I can tell you there is a very active community around Adobe Flex, which uses a combination of XML based syntax for UI development coupled with AS3 on the code behind. I can't stress how great the resources and community are. If you're not a designer, and you just want to build applications with Flash and ActionScript then Flex is a great place to not only start, but really grow your skill set. It also helps that the SDK is free, and open source.
Check out these guys for code and news:
Colin Moock's Essential ActionScript 3.0 is great. This guy is a both a wonderful programmer and a wonderful writer, the book starts off very very simple, but it covers a huge number of topics.
For a very well done and down to earth beginners guide to Actionscript3 you must check out "Learning ActionScript 3.0" by Rich Shupe and Zevan Rosser. This is an ORIELLY publication, which are my favorite. It was suggested to me that I read this book before reading Colin Moock's "Essential ActionScript 3.0". After reading "Learning ActionScript 3.0" you will have a solid understanding of the new Display object and Event flow which are two very important areas to tackle. Next I would move onto "Essential ActionScript 3.0" which is very comprehensive and informative. Once you are feeling serious about the language and want to attack deeper OOP principals then it is time to check out "Object-Oriented ActionScript 3.0" published by Friends of Ed which goes over many things including UML, design patterns, inheritance, encapsulation, polymorphism, interfaces and more.
For online reference my favorite is Lee Brimelow at http://www.gotoandlearn.com and http://theflashblog.com
Reading books and tutorials is great, but nothing beats getting into the IDE and applying new concepts and ideas and confirming the results. Get in there and start tracing stuff :)
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If you're already familiar with basic programming concepts, I recommend Advanced ActionScript 3 with Design Patterns by Joey Lott, Danny Patterson.
The absolute best book on ActionScript is hands down Essential ActionScript 3.0 by Colin Moock
this website is quite good if you want to learn about AS3 games!