The key to great facial hair: know the basics. These tips should be a foundation for how you prep, trim and manage your preferred style. Learn them. Apply them. Look your best.
Experiment with shapes that look best with your facial features and also work with the time you want to spend maintaining said style
Thickness can be managed with a snap on length guide comb or an adjustable length guide comb
Longer around the mouth styles should always be trimmed in the direction of hair growth
Shorter around the mouth styles can be trimmed with or against hair growth
Make sure to use the detail blade, available with many Wahl trimmers, to get into tight spaces and create tighter lines
Always clean up loose or long hair around the lips
Some goatee-esque styles require attention every couple of days while others only need re-shaping a few times a month