If you have light menu pages but heavy graphics on pages deeper into the site, sneak a graphic or two into the user's cache while he or she is reading your home or menu page. To do this, set the graphic's height and width to 1 (so it will be barely visible). Then, drop the tag anywhere in your light HTML document.

Example:
<IMG SRC="image.jpg" HEIGHT=1 WIDTH=1 ALT="image">