Reddit reviews The Essential Guide to Flash Games: Building Interactive Entertainment with ActionScript

First, I would say spend some time prototyping what you want with simple shapes. Experiment with what you can do and how you want to do it. Once you're satisfied with what you can do, breakdown the game into smaller tasks and list those out with target deadlines. Try to stick to one thing until it's done and move onto the next one. Smaller goals are easier to achieve and will give you the confidence and enthusiasm to keep going.

As for technical stuff, I would say read up on object oriented programming and programming design patterns. There are a few books out there that are specific to AS3 and explain the most common patterns well. Be careful though not to use design patterns for their own sake. Each pattern is meant to handle specific cases that arise commonly.

Finally, I would say don't try to re-invent the wheel. By this, I mean don't try to program your own engine, etc. There are several very good Flash game engines out there like Flixel, FlashPunk, etc. Leverage what you can from those so you can focus on your game. Also, have people play it early and often so you can get feedback and make changes. It's easier to make changes earlier in the process.

EDIT: As far as forums I have been a member of the following forums/blogs for years and they have a plethora of information:

gotoAndLearn

Kirupa

8-bit Rocket author of this book

> to go on my website

Actionscript (or haxe) is a good idea then, because with flash you avoid the "download barrier".
Depending on your level of knowledge there are different books for actionscript that are interesting. As you seem to be starting out you might want to look at The Essential Guide to Flash Games.