To keep your stubble looking stylish, not scruffy, trim it every day. Your goal here is not beard growth per se but even stubble is a beard style that needs proper attention to acheive the right look.
Stubble Beard Trimming
1. Clean shave the area of your face and neck leaving only the hair in the area of your future stubble mustache and beard.
2. Set the length setting on your beard trimmer to the shortest setting (0.4mm).
3. Trim your beard in the opposite direction of hair growth. To keep your stubble looking stylish, not scruffy, trim every day.