One thing that is totally gross, is over plucking, which I for one have been guilty of in the past, it is not cute, nor pretty and girls in your teens please just embrace your natural brow. You will thank me for this advice in your 20's ... I promise, please look below for insane examples
Instead of filling in sparse hairs with a pencil or powder, have them professionally tinted one shade darker than your hair color, then using gel to define every hair in a more natural fuller way.