Wash and dry your beard first
Comb the beard downward to see its natural shape
Find the neckline by placing two fingers above your Adam’s apple
Imagine a curved line from behind one jawbone to the other, passing above the Adam’s apple
Trim everything below that line
Use a trimmer with a guard first if you want to avoid cutting too high
Shave or trim the lower neck area cleanly
Keep the line smooth and even on both sides
Check both sides in a mirror for symmetry
Clean up stray hairs with a detail trimmer or razor
Recheck the neckline after finishing to make sure it looks natural