It is possibly a gross oversimplification, but in general softer things grip better. So softer tyres, softer inserts, softer springs, softer shock oils, etc.
Another potentially gross oversimplification is to say that you can tune for understeer or oversteer by moving your grip bias backwards or forwards.
So therefore, as a broad starting point, to make your car under understeer less, you can fit softer things to the front or harder things to the back.
My apologies if I was stating the obvious, but you did ask for general advice!