Make sure any placed are is linked, not embedded. That will just needless increase the file size.
If you have already embedded the links, pull up your Links panel, select a link and in the flyout menu choose "Relink...". Then choose the external file again but be sure to check the box that says "Link" before hitting ok.
You may want to save the file WITHOUT a PDF preview. To do this, choose File->Save As... then hit OK. In the Illustrator Options window that comes up, uncheck the "Create PDF Compatible File" option.
That should dramatically reduce the file size.
"Great spirits have always encountered violent opposition from mediocre minds." -Einstein