I am a two month veteran to hanging.
My advice to a newbie would be to go toward "more sag!!" It seems that more is required than is intuitively guessed at.
I don't honestly know what happens when you have "too much" sag. Stay within the limits of how high you can reach to hang it and touching the ground when in the hammock and you'll be in the ballpark
Comfort comes from being diagonal.
Too snug and you can't get diagonal and experience shoulder squeeze.