Step 1:

Measure the width of your eye by bringing your false lashes to your lash line. Line up the inner corner of your false lashes close to the outer edge of your pupil and end your false lashes at the outer corner where your natural lashes stop.

Step 2:

Mark where your false lashes should be trimmed by using your tweezers to pinch the outer end of where your false lashes should end, and trim the excess.