there is no magic bullet. you do have to optimize as much as possible.and test and try and test again.
if you rely more on flash, and not AE, and turn each element into a movieclip, the file size should go down a lot.
as a test, i did a 300 x 250 swf with the elements from your posted banner. the swf sizes i come up with are between 16.5 and 20.5 KB. you can see an example
here ( this wasn't meant to be an exact reproduction, just something to get the gist of it....
the background image was an imported jpg. likewise the car, and the 'Good Chevrolet' sign. these were all turned into movieclips and then animated. the text " Turning the competition upside down' was created in Flash, with the text broken apart, and turned into a movieclip. text created in flash , rather than imported from another program, should be a lot smaller in file weight.
i did one test using only scripted tweens ( used greensock's TweenLite), with the putputted swf asat 20.5 KB ( TweenLite does add a few KB to the file), and i also did a timeline based animation using classic tweens. this file ( which is the one posted) came out to 16.2 KB.
i hope that helps
