There are a number of things you can do; it really depends on how much money you want to spend. You could start by increasing the tyre pressure by three or four psi above the recommended pressure and see if that is enough to do what you want. Beyond that you could fit sportier tyres, you could fit harder suspension bushes, lower the suspension, fit better shock absorbers, and heavier anti-roll bars. If you do want to modify the suspension I would suggest you consult a specialist such as Pedders or K-Mac.