Make sure you have the correct spring for your weight.
Then do the collar down until it starts to create tension on the spring, then add one turn. if you want more preload, turn it a turn at a time. Saw somewhere that mentioned no more than 4 turns? As you should then change spring.
Just have a play until you get the feel you like. Remember the more you wind it in, the less travel you will have as you are preloading the spring.
Two full turns of the spring is the max amount of preload you should have. Any more and youll need a heavier sping, best place i find is just tight enough so the spring does not wriggle. hope that helps