If you are a flash beginner, you should have read A Flash Journalism Presentation by Mindy McAdams which covers very good points about the Timeline and motion tweening. It is very easy for you to learn as the presentation is clearly demonstrated by screen captures.
If you wish to learn further about flash best practices to become a flash professional, there is also another great article written by Jen deHaan from Adobe which covers quite a lot of things in term of organizing ActionScripts, behaviors conventions, screens conventions, video conventions, accessibility, version control guidelines, and optimizations for performance. The article is suitable for beginner or intermediate level.
Related Post: Flash Best Practices part 1