Start with the wing:
If you're struggling with freehanding, try starting with the wing first and then connecting it to your lash line. 
Layer different liners:
Use a pencil liner first for a base and then go over it with a liquid or gel liner for a more precise look. 
Alternate eyes:
Instead of completing one eye at a time, alternate between eyes as you apply eyeliner to ensure the wings are even. 
Clean up mistakes:
Use a cotton swab dipped in makeup remover or concealer to clean up any mistakes or smudges. 
Prime your eyelids:
This helps create a smooth, even surface for the eyeliner to adhere to and prevents smudging.