Depending on your budget, I would suggest the following in order of priority:
1 – Check and replace any worn suspension components such as ball joints, track rod joints, etc..
2 – Replace the front and rear (if you have one) Anti-Roll bars with those from a 944 Turbo.
3 – Replace all bushings with Polyurethane bushings.
4 – Fit Adjustable Shock Absorbers.
5 – Lower car front & Rear (various ways to do this with stock or lowered springs/torsion bars or coilovers).
I’d recommend that you talk with a local Porsche specialist that has racing/autocross experience for their suggestions.