Based on the article by beard care experts at Beardoholic.com
Trimming the beard starts once you surround yourself with the necessary tools: mirror, beard trimmer/clipper, comb/brush, shaper, scissors, and oil.
Some beard styles look better on certain face shapes, so determine that first.
Do this by measuring the distance between cheekbones, forehead, and jawline, and then between the chin and crown. The longest measurement shows how is your face shaped.
If you have round or square face cut the sideburns and cheeks shorter and leave the hairs on the chin longer.
For those with oblong, triangular or rectangular face trim the hairs on the chin, and leave the sideburns and cheeks thicker.
Let the cheek lines grow naturally or sculpt them with a curve or step cut.
The neckline should be two fingers above your Adam’s apple. Shave all hairs below that line.
Men with shorter hairs should blend the sideburns with the hair, while those with longer hair should let them grow above and below the ears.
Set the trimmer to the longest length attachment and work your way down to even the hairs out.
Identify moustache length with beard comb and trim with beard scissors by following lip line. Apply beard oil to moisturize the skin and beard.