I autocrossed my '84 duke for four years, and I'm now into my second year of using my '88 Formula.
So far we've mentioned tires (absolutely #1), front and rear sway bars, lowering springs or coil overs. I'll add that using cut springs to lower/stiffen the suspension is fine as well when done properly.
I'll also add that it's best IMO to try and stiffen the front
a bit more than the back. To that end I've used poly bushings and Rodney's zero lash end links with the front
sway bar. On the back I've retained the use of rubber bushings for the sway bar and end links.
And moving the battery up front also helps the balance and handling of a Fiero.
I like this camera angle of one of my runs last year. This was a more wide open layout than we normally have, which resulted in higher than usual speeds for an autocross event. I was going about 70 MPH when I entered the stop box.
[This message has been edited by Patrick (edited 05-10-2015).]