Some more expensive bike forks actually have both compression and rebound damping. There are so many models out there now, the best overall advice is to keep the suspension system clean. For more detailed maintenance information, consult your Owner's Manual or a reputable bike shop. Today's forks are much easier to maintain than they were ten years ago. This allows you to adjust, or tune the spring rate to the weight of the rider.
Spring rate is how much force is required to get the spring moving.
A heavier rider will require a higher preload adjustment than a lighter cyclist. Please read this regarding the terms of your use of this information.