adjust the collars so that the spring is not loose(has zero vertical movement) and that is 0-preload. If you feel the need to, you can tighten it up more to run more preload, but me personally I run 0. I like to get as much travel as possible. Hence why adjusting ride height with the brackets rather than the springs is ideal.
1992 RPS13- Built SR20, GT2871r, AEM EMS, 21psi, 275/50 ET Street Radials