Use symbols, animated or otherwise, for every element that appears more than once.

Use tweened animations whenever possible when creating animation sequences. Tweened animations use less file space than a series of keyframes.

Use movie clips instead of graphic symbols for animation sequences.

Limit the area of change in each keyframe; make the action take place in as small an area as possible.

Avoid animating bitmap elements; use bitmap images as background or static elements.

Use mp3, the smallest sound format, whenever possible.

Group elements.

Use layers to separate elements that change during the animation from elements that do not.

Use Modify > Shape > Optimize to minimize the number of separate lines that are used to describe shapes.

Limit the number of special line types, such as dashed, dotted, ragged, and so on. Solid lines require less memory. Lines created with the Pencil tool require less memory than brush strokes.

Limit the number of fonts and font styles. Use embedded fonts sparingly because they increase file size.

For Embed Fonts options, select only the characters needed instead of including the entire font.

Use the Color menu in the Symbol Property inspector to create many instances of a single symbol in different colors.

Use the Color panel (Window > Color) to match the color palette of the document to a browser-specific palette.

Use gradients sparingly. Filling an area with gradient color requires about 50 bytes more than filling it with solid color.

Use alpha transparency sparingly because it can slow playback.