I am not sure what you mean--do you have some pics? I would guess that part of the problem is simply knowing when to stop. If you set the head aside for a few hours or days it generally gives you more perspective.
There is really a lot of variety in the "newborn" look. Not all newborns are sparse. My sister was born with a full had of black hair (which later fell out). I've seen babies who are brand new with *thick* hair. I was born blond and was dark by age 5. But I actually look bald in most of my photos. A friend who just had a baby in December has almost no hair and what hair he does have is about 1/4 of an inch long!
Using one of the 40-43 guage needles with 3 barbs is how I do mine. That way I can still root only 1-2 hairs at a time close enough to give me good coverage but not so thick that it's a lot of hair.