There is a thread on this already but I would organize my mod into 4 groups.
First would be sways, suspension, exhaust, and intakes.
Second would be oil cooler, 4.08 final drive, and CSC/clutch/flywheel upgrade.
Third is a tune. An aggressive tune.
Fourth would be a nice body kit and a set of wheels but this is subjective.
[Official] Which 1st mod(s) for my Z thread.