Start with the basics, bushings.
Bushings, or spherical bearings, are used to transfer energy. Imagine hitting a rubber block with a hammer versus doing the same with a steel block. The energy transferred between the harder compound transitions better. Manufacturers are held to NVH standards, you can read more about it here if you want to understand why your (newer) car doesn’t sound like it’s about to lose a wheel every time you hit a pothole.
There are lots of reasons you want to get rid of soft rubber bushings from your suspension. One of the largest is because it reduces energy transferred to your shocks. What this means is, you can put $2,800 coilovers on your car but if you can’t channel the energy correctly to those coilovers, you’re not getting the most out of your suspension. Another large reason to eliminate the slop of rubber bushings is your alignment. Not only tire alignment but suspension component alignment. soft bushings allow control arms to twist and flex in undesirable directions before transfering the energy to the shock. You can feel this in the amount of time it takes the car to take a set or transition from one direction to another. In some extreme cases (like c5 corvettes) when a grippy tire tries to stick to the road and resist turning you can lose over 1.5 degrees of your static camber. This means you have to run much more aggressive camber on a stock bushing car so that when a soft bushing flexes you remain in the desired camber range. With stiffer bushings your alignment settings can be held much closer to optimal at all times.
Start by removing slop from your suspension, that’s your first step.
Read that. Read it again. Did that make sense?
You can have too much spring, or you can have too little. Choosing the best baseline rates to start off with will make a bigger difference than spending an additional $1,000 on shocks.
Check what Optimum G has to say about ride frequencies
All of their articles are phenomenal, and I suggest sitting down with a pot of coffee reading through all the knowledge they have to share.
The chart listed above suggests passenger cars adhere to a ride frequency between .5 to 1.5, and high downforce vehicles are closer to 3.0-5.0+hz.
Follow that link to develop the spring rates for your car.
As a baseline, I requested BC Racing to send me a set of 10F/12Rkgs springs with RM style shocks. My Time Attack EVO is using an Affinity Aero TA78 Wing along with a homebrew 80" front splitter mated to a Voltex front bumper.
The car tends to oversteer slightly until roughly 80-90mph where once enough air is flowing through the rear wing, it settles the rear allowing for a new world of grip.
Having your shocks matched to your spring rates is important, and making sure your spring rate is linear throughout the stroke helps build confidence in your suspension.
This tends to get most people 80% of the way there, at the very least it’s an improvement over what they’re replacing. Just because you buy aftermarket suspension does not mean you’re improving grip, it could quite possibly be the opposite. I’d recommend you do your research and ask questions, the technical support from BC Racing is extremely useful if you have any questions. An explanation of roll centers, tire setup, and digging into aero might be added in the future depending on popularity.