Natural lashes are not like a strip lash, there is not one single row of lashes, there are lots of layers across the eyelid. Some are more obvious then other but its important to understand lash layering to create a gorgeous top line or even to create a set of wispy lashes
Perfecting the Top Line
When mapping out the style of lashes you are going to be doing, to get a perfect line you will also need to write a mm shorter underneath the normal mapping length and a mm longer just above it
Once you've got your head around lash layers you can completely reverse the rule to create a really dark, dense lash line. Apply shorter lengths on the bottom layers and longer on the top, you will create a gorgeous dark lash line at the base, but the ends will be lighter giving a wispy look.
Blending you Lengths
To keep the difference in length looking smooth and avoiding a step in your transitions, its important to only increase or decrease 1mm at a time. Even if you're working with super short lengths in the inner corners and you've got to change lengths really quickly, you still need to follow this rule.