I am kinda new to AS 3 development.. and the thing is I am always getting into problems how to structure the different views of an application state?
Do you use a MVC framework for this? I have looked at some puremvc, robotlegs but our flash projects are usually relativly small so I wonder if it is not a overkill :)
Design patters are good as long as you don't try to use them for the sake of using them. I always have my views separate to model as it is, but rarely work on something big enough to warrant a flow blown implementation of something like PureMVC. On large projects then yes they can be beneficial. The hard part is deciding how "big" is big enough to use them. Probably comes down to experience to make that judgment.
Anyway just make sure objects are loosely coupled and that your model and view are not one and the same. Quite often instead of extending a MovieClip I prefer to use composition and have a class have a MovieClip. For me I think it helps separate visuals from the data.
A framework can be particularly valuable if you intend on handing the code off to someone else. Whatever framework you choose, you'll introduce a common set of expected relationships from which someone can build an understanding of the codebase.
If the view logic is largely sequential, or at least modal, an easy non-framework mode of organization is to group your views into "pages" and have a single controller manage which page is on-stage at a time and feed in model data from wherever.
To be honest I'm not a fan of applying traditional design patterns to Flash development. If you're writing pure classes then you can do anything you like, but if you're linking classes to visual elements (like MovieClips), I find that the proper way to structure things (i.e. the way that best avoids duplication of effort and preserves separation of concerns) winds up being dictated by how you need to stack and/or nest your display timelines.
In other words, I find it better to work out at the display level what things ultimately will need to be in the same or in different timelines, and what will ultimately need to be nested or not nested, and then work out which classes should extend or compose each other afterwards.
But note that this is all assuming you're making stuff where the logic is closely coupled with the display elements, which is what I consider the area where Flash shines. Naturally if you're making a loan simulator with no animations or skinning or whatever, it's sensible enough to just use an MVC pattern and then slap a static display layer on top, with each button pointed to a C and each text box pointed to a V. But then that's exactly what you'd do if you were making the same thing in Java, or as a JS-powered HTML form, or whatever else. The advice in this answer is what I find works best when you're making the sorts of heavily visual things that would be ill-advised to attempt in anything but Flash.
if you are really new to AS3 and are planning to do "pure" coding (neither using the graphical approach promoted by the Flash authoring tool, nor diving into the Flex world), i suggest you don't waste your time on AS3 and move on to haXe ...
haXe is not very well known, so the only opinions you'll get are from people using it ... there's a little bias of course, but you may read their statements here, here and here ...
now when it comes to patterns and framworks, there are many possibilities ... design patterns are solutions to a set of problems ... do not make the mistake of trying to transform all the problems you encounter into problems that fit the patterns you know ...
in my book, there is one fundamental principle for software design: DRY & KISS - I admittedly still have a lot to work on the latter ... :) ... for more concrete and guiding principles, I stick to SOLID and GRASP ... if your read them carefully and reflect upon the (good) patterns you know, you are likely to find out, that they incorporate said principles ... do not overuse patterns ... do not overuse any tools in fact ... use whatever tool is the best for the job ...
IMHO, pure AS3 is for geeks ... and I love doing pure AS3 ... or at least I did ... it is however uneffective and unrewarding over time ... it is good for developping frameworks and libraries ... but nor for apps ... haXe is good for distributed cross-plattform apps (and for geeks), Flash Authoring approach for "fancy" visual apps, and Flex for classic apps featuring prevalant UI concepts ...
greetz
back2dos