Get some old engine oil, jack up the car, and pry the leaves apart with an old screwdriver or similar, lather the oil in between the leaves.
Do this on all the springs and see how it feels.
Usually makes a huge improvement.
Be aware, I fitted lifted spring packs can lead to hard suspension, as a spring with a deeper arch usually is a harder spring, so it holds the arch.
If you want to get really trick, strip the spring out, and dismantle it, and get some teflon sheet, cut into strips, and rebuild the pack with teflon in between each leaf