Depends how much you want to spend...

Easiest is Anti-roll bar, even just changing the bush from rubber to polyurethane will improve the handling a lot as the ARB can work to its full capability.

On comparison strut brace didn't help that much (although i have installed it on my car )

Brake fluid.... I change it every year... and I do it myself so i know how the condition of the brake fluid is like..