Look at the EnterFrame event and the Timer object. EnterFrame can be used to call a function once each frame, so the timing corresponds to the frame rate. A Timer object can be used to call a function at a rate that you set.

Most new users of Flash start animating using the timeline. You can use it or not, when the .swf file is compiled everything is converted to code in any case. If you are comfortable building a timer as a control for your animation, then use that. You will have more flexibility.

If you can create your artwork as vector rather than bitmap, you'll save file size for the download. Flash can more efficiently animate vectors than it can bitmaps. If you use bitmap images you may find that using gif or jpeg file types may save you some file size. You can use Photoshop's "Save for Web and Devices" option to get the most compact file size while maintaining image quality.

The complexity of the vector greatly matters in saying that a vector is less overhead on a mobile device than a bitmap. Size-wise it is far more efficient but certainly not always in performance cost.

In almost all cases (especially text), vectors will kill your processor. I'm presuming you're not getting into any Stage3D or really utilizing the GPU. With the CPU, bitmaps are almost always faster because it's just copying areas of memory, not calculating. The only case to be made is setting a complex vectors cacheAsBitmap to true and then you have a bitmap in memory anyhow.

If you've built websites before, try to use the cutting techniques you've learned to break the interface up into the smallest bitmaps possible. For instance if you have an interface that surrounds all edges of the screen with the center transparent, it's more memory efficient to cut the bitmap into pieces while removing the transparent area rather than render a single bitmap with transparency.

Mobile devices greatly lack on CPU and you should always think of everything except the latest generation of quad core tablets as basically glorified phones. You're much more used to desktop programming and performance and mobile performance without utilizing Stage3D will certainly suprise you, for the worse.

A Timer is better than Event.ENTER_FRAME. You can't guarantee the framerate during a game on mobile devices which goes up and down. Event.ENTER_FRAME is very expensive so use it a little as possible. Timers are much less expensive and logic executes more reliably over uneven frame rates.