Generally, each layer shouldn't have to be more than four frames long. Without going into long, complicated code samples to show what we mean, here's a look at what each frame should include.
Frame One: Here is where you need to set all global variables. This is important so these can load right when the movie starts. Don't set the playhead to return to frame one. Everything's taken care of from here on and out and there's no reason for it to return.
Tips: Use a "MovieClipLoader" to help you get status information on all the elements in the Flash file as they are loaded. Use the StyleSheet class to allow control over text elements and other styling issues. If you're using Flash version 8 or higher, you can also use Filters to apply different text appearances such as a drop shadow to your text while still keeping it dynamic. Using Photoshop to create a text image with this effect will take the dynamic element away.
***Do not load elements created outside of Flash for the site into the Library for use in Flash. This will make updating the website much easier later, and will be very helpful to someone without any knowledge of Flash who may end up updating the website if you're surrendering control to a client after the design is done.***
Frame Two: This frame will call for external files used to create the website, using XML. This will load the navigation buttons.
Frame Three: This frame will load the CSS file used to control the style of the website.
Frame Four: This is the frame where the Flash website will start, and the playhead will remain here for the length of the site visit, because the previous three frames built and called everything we need to load the website.